What do the colors mean?

This app is good. I got this app because of Shane. But what Im curious about is the colors. What do they mean? The colors Ive seen so far are blue, red, green, and I think yellow as well. If anyone knows text me on my kik: CuteBerry8240. Please help me out

NatsukiTachi about Ghost Radar®: CLASSIC, v1.9.119