Green - VFR (Visual Flight Rules) more than 5 Nautical Miles of Visibility, Ceiling is greater that 3,000 Feet AGL.
Blue - MVFR (Marginal Visual Flight Rules) 3-5 Nautical Miles of Visibility, Ceilings are between 1,000 Feet and 3,000 Feet AGL.
Pink - IFR (Instrument Flight Rules) 3-1 Nautical Mile of Visibility, Ceilings are between 500 Feet and 1,000 Feet AGL.
Red - LIFR (Low Instrument Flight Rules) <1 Nautical Mile of Visibility, Ceiling is below 500 Feet.
Mark has a series of Tutorials that will help you further understand how METARS work.
DeerCrusher also has a Tutorial on understanding the colors as well 🙂
Have a great one!