SERIOUSLY? You generating new string every time using CONCATENATION? Not even using StringBuilder? Not saying about optimization and using char[]. No wonder then that you get a load of garbage collection and losing performance. That's cheating benchmark.

All color combination examples in this article in fact are disgusting...

You are "saving" allocations, but bloating bytecode with inline functions. Is it worth it? And if you remove the inline modifier, there will be allocations for lambdas. Just let the GC do the work.