The red color is due to the red sauce from fermented tofu aka "tao hu yi"
Most normal yen ta fo shops just get the off the shelf type and serve. Good shops will cook the sauce with other ingredients. That explains why most peope end up eating not aroi yen ta fo.
This is my number 1 favorite in Pattaya. 10 years patronising this shop.
Number 2 on my list.
The locals way of ordering Yen Da Fo is:
(Fo )(Yai/Lek/Mi/Mi Lueang) (Nam/Haeng)(Thammada/Piset)
skip the words "Yen Ta", follow by noodle type, and then soup or dry, and finally regular or large serving
Yes, some people like Yen Ta Fo dry.
for example, If I want to order "Big Yen Ta Fo Been Hoon Soup", I just say "Fo Mi Nam Piset". But usually I just said "Muean Derm" (as usual) at the regular shops.