What do you mean not sticky?
As in hardened and slide right across any table or whatever you put them on or fall off the shell a lot?
The latter is solved by get scalpel, get double sided tape, use scalpel on tape.
The former you could possible solve yourself depending upon how it happened, though that can get more fun with chemicals than might be ideal.
As far as colours to pick then as a general rule we call me to make things work (or tell you why it no long works or will fall over), call literally anybody else to make them look pretty. I will say though you could also make your own feet easily enough (these are all straight lines rather than something you would want to use a machine to cut) and a sheet of some kind of rubbery material enough to do this is not going to be a lot.
On colours though then can link up things like
https://www.designmantic.com/blog/infographics/the-10-commandments-of-color-theory