In MCGA, Tell color of pixel in coordinate

I'm unfamiliar in how I could tell the color of a pixel for a specified coordinate.  I am familiar in how i could do this if i was in text mode:

If Chr(mem[$b800:position]) = 'x' then

Where 'position' is the value for the coordinate, and x is the character that i'll do something with if it's there.  This works for text mode, but how would I do a similar approach in MCGA?  Would the $b800 thingy be different?  I know the Chr thing wouldn't work, obviously.  And I assume instead of having the 'x' you would have a color between 256.  But I don't really know, that's why i'm asking  (:

Thanks

PS:  I hope i explained what I would like to know how to do good, if not please just leave me a comment asking for some more clarification...