I am here!
OK as far as I know, tanks were mostly used within the central Luzon area except of course when MacArthur returned (known as the Leyte Landings)...twhere anks rolled from the beaches in that eastern Visayas area.
The central Luzon area was basically becoming a developed area at the time of the war since it is where Manila is and roads (dirt, gravel and concrete) have been constructed. While red to red brown clay is abundant, this type of material is not popular in road constructions because it is not so permeable and retains water for longer period. Usually soils with colors ranging from light to dark brown (from bassalt) are used because of better resistance to abbrasion and good permeability.
Being in construction, I can say that mostly the most common color for dirt will be light to dark brown. I really don't see much red to red brown soil in my projects within Central Luzon.
Here's a colored picture of a Sherman in action in Manila ( a future diorama project of mine) for reference.