For example, like set the top ten layers of patches blue to make the sky?
You can use an "ifelse" or "if" statement. For example is used
ask patches [if pzcor = -16 [set pcolor 36]]
ask patches [if pxcor > 5 and pxcor < 12 and pzcor = -16 [set pcolor blue]]
to make the ground and a river!
You can use the < and > signs and write the intervals that you want. For example
if pzcor <= -13 [ set pcolor brown - 3 + random 3]
if pzcor <= 13 and pzcor >= 10 [ set pcolor brown - 3 + random 3]
try if this works
ask patches with [pzcor = -16 ]
set pcolor blue + random 3
and then repeat maybe
If you are looking to change the color of some patches, you also use:
if random 100 = 0 [
set pcolor list [0 0 255 30]
This is for a more translucent kind of look.
that worked for me.