Kesariya Balam is a very popular folk song of the desert Thar and the earliest known popular version was sung by Padam Shri awardee folk singer Allah Jilai Bai in the Durbar of Maharaja Ganga Singh ji.

Allah Jilai Bai (1 February 1902 - 3 November 1992), Born in Bikaner to a family of singers, by the age of 10 she was singing in the Durbar of Maharaja Ganga Singh. She took singing lessons from Ustad Hussain Baksh Khan and later on from Achhan Maharaj. She was well versed in Maand, Thumri, Khayal and Dadra. Perhaps her best-known piece is Kesaria Balam. In 1982, the Indian Government awarded her the Padma Shri in Arts field, one of the highest civilian awards. She has been also awarded by Sangeet Natak Akademi Award in 1988 for Folk Music.

TL;DR
Kesariya Balam folk song is about welcome of Rajput Warriors on their return to home after fighting wars away from home by their wives.

Inspiration

Dhola Maru

The kesariya balam song is inspired by story of Dhola and Maru and Rajput bravery, sacrifice and traditions and The desert, Thar.

You should read the story of Dhola Maru here, It's quite a fascinating tale.
Read: Dhola Maru Story

Original composition, meaning & lyrics of Kesariya Balam

Below is 'Kesariya Balam' by Allah Jilai Bai

केसरिया बालम आओ नि पधारो म्हारे देस
नि केसरिया बालम आओ सा पधारो म्हारे देस

पधारो म्हारे देस, आओ म्हारे देस नि
केसरिया बालम आओ सा पधारो म्हारे देस

मारू थारे देस में निपूजे तीन रतन-2
एक ढोलो, दूजी मारवन, तीजो कसूमल रंग

पधारो म्हारे देस, पधारो म्हारे देस नि,
केसरिया बालम, आओ नि पधारो म्हारे देस

केसर सू पग ला धोवती, घरे पधारो जी..
हे केसर सू पग ला धोवती, घरे पधारो जी..

और बढ़ाई क्या करू पल पल वारू जीव
पधारो म्हारे देस, आओ म्हारे देस नि
केसरिया बालम आओ सा पधारो म्हारे देस

आंबा मीठी आमरी,
(आम से भी मीठी ईमली.)
चोसर मीठी छाछ.
(और सबसे मीठी छाछ)
आ..अलाप
नैना मीठी कामरी
(सुंदर आँखो वाली कामिनी)
रन मीठी तलवार
(और युध में प्रिय तलवार..)

पधारो म्हारे देस, आओ म्हारे देस नि
केसरिया बालम आओ नि पधारो म्हारे देस
पधारो म्हारे देस, आओ म्हारे देस जी
केसरिया बालम आओ नि पधारो म्हारे देस

'Kesariya Balam' means: Balam, means lover and the term Kesariya Balam is used here to distinguish that this lover is a Rajput. Consider this song as if Maru is calling her lover Dhola. Or to be exact the wife is missing her Dhola(Husband), who was fighting wars far from home. He is now now returning home, So she is preparing to welcome her husband "A Rajput Warrior" to come back to her, to his own home. Kesariya Balam is a perfect example of Rajputana Royal folk song.

Most people do not know the correct meaning of this song and why is it even special. They just think that the 'Kesariya Balam' song can be used to invite everyone to come and visit Rajputana. While it's actually about Rajput Warrior's return and his welcome in his own home. In Rajputana, only Rajputs used to take part in wars and they would die protecting their land and honour. Kesariya, saffron color represents sacrifice, bravery, purity. That is why they mostly wear Kesariya Safa(Turban) and specifically on Ceremonial occasions. Rajputs besides Kesariya also wear chundadi, leahariya and rarely white safa. Other castes in Rajputana mostly wear white, green etc. Other castes or tribes do not wear kesariya safa, it's exclusive color of safa of Rajputs. And thus kesariya color became symbolic of Rajputs. Rajputs used kesariya color in their clothing, dress, safa and even coloring buildings, architecture etc. Many folk songs of Rajasthan have references to Rajputs or are based on Rajput tales of heroism, bravery, sacrifice, traditions, culture or romance, such as moomal, kesariya banna, ghoomar, jad dekhu banna ri lal pili akhiyan, kallali, Bhalo Chinayo Bhatio, Dhola Maru and many more.

Over time after independence people changed the original composition and they modified the lyrics completely. Only keeping the words kesariya balam. Some of these songs sung by some famous singers and just repeat Kesariya Balam on loop with a lot of aalap, there is nothing else to it. They specifically remove the verses which references "Ran mithi Talwar', so that it can be used as a song of invitation for everybody, and thus it creates a confusion about the meaning of kesariya balam. The current situation is that current generation doesn't even know what Kesariya balam means. They take the meaning literally. that's kesar means saffron and balam means lover. But it's much more deeper than that. It represents Rajput Love, sacrifice, desert, culture and folklores of Rajputana. To know more about Rajputs please read below quotes

Some quotes about Rajputs of Rajputana

The duality in the Rajput character was really astonishing. On the one hand he was a grim warrior, forever ready to draw his sword taking the cruelty, horror and pain of war in his stride. On the other hand he was gentle, warm in his hospitality, a lover of music and dance, and kind to the womenfolk, even those of his enemy. — M. S. Naravane in The Rajputs of Rajputana: A Glimpse of Medieval Rajasthan
The Rajput race is the noblest and proudest in India, they are of highest antiquity and purest descent, they have a military autocracy of a feudal type, and "brave and chivalrous, keenly sensitive to an affront, and especially jealous of the honour of their women".
— Lt.Col. James Tod in Annals and Antiquities of Rajasthan
If devotion to the fair sex be admitted as a criterion of civilization, the Rajpoot must rank high. His susceptibility is extreme, and fires at the slightest offense to female delicacy, which he never forgives.
— Lt.Col. James Tod in Annals and Antiquities of Rajasthan
If we compare the antiquity and illustrious descent of the dynasties which have ruled, and some which continue to rule, the small sovereignties of Rajasthan, with many of celebrity in Europe, superiority will often attach to the Rajput.
— Lt.Col. James Tod in Annals and Antiquities of Rajasthan
In the ancient days the Rajput principalities were India's stoutest bulwarks against foreign invasion. Khshatriya armies fought not only Alexander and his Greeks, but also the hordes of Scythians and Bactrians which poured into India up to the end of the 1st century.
— A. H. Bingley in Handbook on Rajputs
Ten thousand Muslims fell in the onset, which cost seventeen hundred Rathor, besides Guhilotes, Haras, Gaurs, and some of every clan of Rajwarra (They are all names of rajput clans). Aurangzeb and Murad (Moghul Kings) only escaped because their days were not yet numbered. Notwithstanding the immense superiority of the imperial princes, aided by numerous artillery pieces served by Frenchmen, night alone put a stop to the contest of science, numbers, and artillery, against Rajput courage.
— Annals and antiquities of Rajasthan
"Tarni Tapi ne kariye Chai do, te che ruda Rajputo ni reet re!"
— A saying about Rajputs
The meaning is simple, "To stand firm in the heat of the desert sun, so that others may take relief from the heat in your shadow is the true characteristic of a Rajput!"
A Rajput would rather die than break his promise.
— Swami Vivekananda

And Letters between Maharaja Ajit Singh & Swami Vivekananda

More information about Rajputs can be found on following link. Rajput Provinces of India : A catalogue of all the Rajput Princely States and Thikanas of Rajputana

Conclusion and Song recommendations

Folk music is suffering from cruel editing. People say that they are keeping folk music alive by remixing it, modifying its story, context and even lyrics. I think that is the perfect way of destroying something of historical importance, be it culture, heritage or traditions. And folk music is india's heritage and it should be presented without modification in its soul or essence. And if this editing continues it'll create confusion, ultimately destroying folk music.

Some song recommendations:

I hope you liked this post. Thanks for reading this far.