Couple of different ways to do this. The easiest is to use the latest version and the color_statistics module which includes a SUM_R, SUM_B, SUM_G which is probably what you are looking for.
Alternatively, you do have pixel access to the image via the VBScript module (see GetPixels routine).
Or you can use the API to read the current RR into another app in a RGB triplet format.
Or you could use the Sample Color module
to select an area to read. This produces a couple variables that represent the average of the pixels in the selected area.
There are probably many more ways but I think we got what you needed in the first para. :-)