You could try the tolerance setting on the brush that you use.  The higher you set the figure the 'more' colour it replaces.  Let's say that you have dark red, light red, medium red and slightly-darker medium red.  If you set the tolerance setting to 5 or 10 (with the colour as medium red) it will replaced the medium red and the slightly-darker colour.  If you set the value to 30 or 40 it will probably replace all of them.

Alternatively you could use the 'cut and paste' functions to cut out the bits of the house you want to paint, put them on a new layer and then, on the top layer, simply use the 'colourize' function.

If you need any more help gimmie a scream, I would be more detailed but I have to go VB training!

=)

PetitPal.

Just a thought ...

You might get some ideas via Colours/Adjust/Gamma Correction.

Happy painting!

LRH

Hi :)
the above comments you can use, also, I do this all the time:
select the chunk which you want to re-colour with the selection tool... you can use the rectangle one in the tool options to select most of it.. and select the rest by changing the shape if it helps.... and.. holding shift and selecting more (adds to the selection) and holding control while selecting removes selection... anyway, do this and then colourise it... or else adjust hue/sat/gamma...
these are all in the colour toolbar option :)

this way might be a bit fiddley, but i always do it ^-^'
Hope that's of help :)

Seeya!
  Kitten ^_-