The colors correspond to certain blood glucose levels. Black is over 500, red is 400-499, pink is 300-399, yellow is 200-299, blue is 100-199, dark green and lime green are the only ones that are different depending on the type of meter.
On the AlphaTrak, dark green is 68-99....anything under 68 is lime green and your "time to act". That's getting too low so you want to get his number up.
On a human meter, dark green is 50-99...anything under 50 is lime green and again, the "time to act" to do something to get the blood glucose back up to a safer place