Learn French: Sont-ils prêts à porter des survêtements kaki ? - Are they ready to wear khaki tracksuits?

Because kaki is a color adjective derived from a noun. In French, colors that come from things like fruits, flowers, or elements (like marron, orange, or in this case, the dusty earth that gives us kaki) are invariable. This means they never change their spelling to agree in gender or number with the noun they describe.

Why do we use à in prêts à porter?

The adjective prêt (ready) requires the preposition à when it connects to an infinitive verb, meaning "ready to do something." Note that if you were connecting it to a noun instead, you would use pour, as in prêts pour le sport (ready for sports).

Is survêtements the only word for tracksuits?

Survêtement (literally "over-garment") is the standard, proper word for a tracksuit. However, in everyday spoken French, you will very often hear the English loanword le jogging used to mean the exact same thing.

Is the inversion in Sont-ils typical for everyday conversation?