How to draw patches situated in crossroads?

Question

How can I draw in red the patches situated in crossroads (the roads are drawn in white) as in the figure below ?

Here is my beginning of code:

ask patches with [ (pcolor = white) and (pxcor mod (nb-patch-length + 1) = 0 ) and (pycor mod (nb-patch-width + 1) = 0 ) ] [set pcolor red] 

Thanks in advance for your help.

Answer 1

How about this? (Assuming roads are one patch in width and are always horizontal or vertical.)

ask patches with [all? neighbors4 [pcolor = white]] [set pcolor red]