I checked the dictionary and found out that red is "aka"
Why does Google Translate turn aka to akai?
Kuruma wa akaidesu
(By the way, why is akai joined with desu?)
Well, it's simple. While in English "red" is both a noun and an adjective, in Japanese the noun is "aka", written 赤 the adjective is "akai", written 赤い.
The fact that it's joined is probably just the way google joins romaji, I'm not sure. Also notice that originally there are no spaces in Japanese so Google probably just tries to make it more readable for people used to western languages that use spaces between words.