BE36 pilot reports inadvertent restricted airspace incursion while attempting to deviate around build ups using using XM weather. The weather depiction obliterated the airspace boundaries on both the MX20 and the G530.

Narrative

I had departed Houston; heading north. The plane is equipped with an MX20 and Garmin 530; each of which paints weather (precipitation) on the screen; and each of which shows airspace borders. I climbed above the base cloud layer so I could see the clouds/small storm buildups. There were several small (green and yellow) cells on the screen; and several moderately tall cloud buildups around. I diverted my intended course multiple times to stay out of any weather issues. These diversions; however; sent me inadvertently into a restricted airspace area (R-3804). I announced on 'Guard' frequency that I was inadvertently in the airspace; and I contacted the nearby Polk Approach immediately (while still in the airspace). I then followed their instructions and exited the airspace immediately. One factor in this mistake is the way the MX20 and G530 paint the precipitation on the screen. Even these modest weather indications (green and yellow) cover up and obscure the usual airspace markings that show up on the screen. Thus when maneuvering to avoid cell tops; the border lines of the special airspace are not visible on the screen. I had been accustomed to (and perhaps too reliant on) the airspace indications on the screen; especially when improvising a course en route to stay in good weather.