There are tons of grip tape colors already in Skate! You need to unlock all the Hedgemont, Gullcrest Village, and Market Mile boxes because that is where all the grip tape colors can be obtained from. In fact, every color of grip tape manufactured in the real world–that I can think of–is already featured in Skate. No need for a grip tape color wheel or anything, in my opinion. Honestly, I'm just thankful there are colors in the game!
During the Skate 3 days (circa 2011-12), in order to achieve a colored grip tape, I went to the Skate.Create site, designed a solid a color graphic, then applied it to my deck in-game in a way such that it glitched to the top of the board, causing the grip tape to appear the graphic color. Then, it was trial and error to achieve the desired color. Not to mention, every time a new emblem was created, Skate 3 required a restart in order for the new emblem to reflect in-game.
Open up those boxes!