This evening we had a line of “storms” move through. The radar showed a large blob of red directly over my area, yet all we got was a little thunder and lightning, a sprinkle, and a few moderate wind gusts. What exactly is the radar measuring/representing?
dopler radar should show the direction of the precipitation. It also has the potential to show the speed. It’s useful when looking for rotating rain/hail.
The actual colors represent the radar beam bouncing off of precipitation. The strength of the returned radar signal is measured in dBZ and the colors are used to represent the intensity of the returned signal. If you go to radar.weather.gov and click on a radar near you, you’ll see a legend on the right that shows 20-30 dBZ as green, or a light radar reflection, and 50-60 as red, a lot of reflection indicating a lot of precipitation. And of course, others in between (and ignore the blue, that’s background noise).
As far as your particular lack of “red” weather, I don’t have a good answer, but it could be that the storm went on either side of you but the image you saw wasn’t “zoomed in” close enough to see a break in the red.
In the spring, my area had one night where there were numerous hail storms that absolutely pounded the snot out of us, but in some it only sprinkled while a few hundred yards away, roofs were ripped off and cars totaled by hail.
Yeah, and with 60 mph winds, the intense precipitation isn’t coming straight down, so even with the intense red cell directly over your roof on a radar weather map, you wouldn’t know if that means that it’s gonna land on your roof.
Doppler radar is usually very accurate (this comment will be followed now by others pointing out its flaws) 
If you can give a location, I can probably try and give a more exact reason why it didn’t rain very hard.
Another factor is distance from the radar. If you are far from the radar, the radar beam sampling the storm can be several to 10k+ feet above ground, due to curvature of the earth. If you are in the southern Plains this year, a lot of that will be evaporating before it hits the ground. Another factor is exactly what radar image you were looking at (base reflectivity (a certain beam angle), composite reflectivity (maximum intensity from all beams). A radar is sampling a storm at multiple levels, from at least 4 (0.5 degree, 1.5, 2.5, and 3.5), to a lot more manually (not sure exactly how this works).