There has been lots of posts over the years regarding to the use of "Pink" Thai IDs cards. Here is my experience after 5 or 6 years of use. In my mind it's second class to your passport or "normal" Thai ID, in so much they are used when a greater level of verification is needed, like banks, AIS, LD (land department). However, I have successfully used the pink ID in Hospitals both private and government, doctors, dentists, which is useful if I need to go without thinking about taking my passport, because I leave it at home.