There's no way of customizing your BMX color like you do with your cars, via Los Santos Customs. Although there's a glitch you can do for this.
Check out this YouTube video, or follow the steps below.
[https://www.youtube.com/watch?v=H2D8ud0Glok]
Open Internet Browser app on your cellphone in-game. [screenshot]
Search for "Pandm" which is the website where you can purchase bicycles in the game (pandmcycles.com). Or select the "Travel and
Transport" tab at the Home Screen. [screenshot]
Select BMX but don't press "Order" yet.
Now press the "Home" button. [screenshot]
In the Home Page press "Travel and Transport", enter "Legendary Motorsports" website and search for the "Truffade
Z-Type". [screenshot]
Choose the color of the "Truffade Z-Type", which will then reflect on your BMX color. Do not press order. [screenshot]
Click on the Search History button. Go back to the bike details. [screenshot]
Select Order BMX. [screenshot]