C would make the call

Reasoning:

C understands that C and D has got to have different hats by this logic:
Red hat = r, white hat = w, (I left out the one behind the wall)
Option 1: w r r r w -> A would call his color
Option 2: w w r r w -> B knows he has white if A doesn't call his color
Option 3: r w r r w -> Same as option 2

C calls white.

C would make the call

Reasoning:

C understands that C and D has got to have different hats by this logic:
Red hat = r, white hat = w, (I left out the one behind the wall) 

Option 1: w r r r w -> A would call his color (three red hats infront)
Option 2: w w r r w -> B would know that he has white if A doesn't call his color
Option 3: r w r r w -> Same as option 2

C calls white.

C would make the call

Reasoning:

C understands that C and D has got to have different hats by this logic:
Red hat = r, white hat = w, (I left out the one behind the wall)
Option 1: w r r r w -> A calls his color
Option 2: w w r r w -> B knows he has white if A doesn't call his color
Option 3: r w r r w -> Same as option 2
C calls white.

C would make the call

Reasoning:

C understands that C and D has got to have different hats by this logic:
Red hat = r, white hat = w, (I left out the one behind the wall)
Option 1: w r r r w -> A would call his color
Option 2: w w r r w -> B knows he has white if A doesn't call his color
Option 3: r w r r w -> Same as option 2  

C calls white.