Combining 2 values in Group By Field on Sum Query

[pcross29]

I've got a table that has 3 fields: CarModel, CarColor and
CarRegistration. I want to summarize the number of records by CarModel
and CarColor. Easy with a sum query:

Group By fields CarColor and CarRegistration and do a count on
CarRegristration.

But what if I want to combine 2 car colors, eg. Red and Blue? I want
the count of all the other colors still, but just want Red and Blue
count combined. Any way to do this with one query?

-- Thanks for looking, Paul