Banned on Multiplayer for what?

I am new to these forums aka just started using them. I just went on FH and tried to access Multiplayer. When I tried, it came up with a message saying ‘Unable to create party session’. Then, another one appeared saying you have been banned from using this feature. I went to Message Centre and saw the message saying ‘You have been banned. Duration of ban: 165hrs. Unbanned: 9/9/14’.
I would like to know, if possible, why I was banned. I don’t really mind too much about being unbanned, as it is only a week long, but I don’t know what I did wrong and so would like to.

Yes, you attempted to sell cars with Designs painted outside the legal realm of the color schemes in the game. Some people think the “glow/chrome/neon/liquid” looks are cool, but they’re violations of the Xbox Live Code of Conduct. Therefore you’ve got a seven-day (168-hour) ban from the time it was placed as a first ban. Second ban is 720 hours (30 days), and third time the person is gone permanently.

Neither bans nor the enforcement of the Code of Conduct are discussed on these forums. If you wish to protest your ban, contact the developers via email at forzafb@microsoft.com. Be aware, because of the email volume your ban will most likely expire before the techs would have a chance to investigate.

Urmm. I have 2 glow cars. I bought the designs for them off the storefront. I. at first, didn’t realise it was a mod until searching it up. When I found out, I kept the cars because it does kinda look cool. However, both my glow cars have their designs off the storefront. I cannot mod myself, nor know how to for FH. I cannot sell/make modded anything. Paintjobs, cars, anything. I don’t know how this was detected as me selling them, as I said, I can’t make them. I will admit I have bought 2 glow designs off the storefront.