What do the colors mean in htop?

For the CPU cores, I think that blue means nice, green normal CPU use and red I/O. But I'm not sure and I haven't found a definite answer.

Then there are the colors for memory. What do green, blue and yellow mean there?

Answer

Press h inside htop for quick help.

CPU

Blue      : Low-priority threads
Green     : Normal priority threads
Red       : Kernel threads
Turquoise : Virtualization threads

Memory

Green         : Used memory
Blue          : Buffers
Yellow/Orange : Cache