BE55 single pilot with a Garmin 530 inadvertently entered Class B airspace; citing the airspace boundaries depicted in the same color as the simultaneously displayed rain caused the oversight.

Narrative

I took off to do some training in VFR conditions. The ceiling and visibility were no problem. However; I have a Garmin 530 with XM satellite weather; which had large areas of light rain (depicted as solid green) throughout the DC metro area. There was no rain in-flight and no rain had been falling on the ground before takeoff and no rain fell on me at any time during that day. Yet; my Garmin screen had many areas of the light green. I knew I was getting close to the Washington Class B airspace but its outline was not depicted on my screen in my area due to the rain depiction using the same color of the Class B lines. Using other references; I suddenly realized that I actually was in the Washington Class B airspace. I turned immediately and exited. I think I was in it for a minute or two. I highly recommend that the FAA work with Garmin to resolve this issue. Garmin GPS displays should NOT be certified to display Class B airspace in the EXACT SAME color that is used for rain. Class B airspace cannot be seen on a Garmin 530 that is equipped with XM weather if rain is in that area.