The safety of plastic is an important thing to be kept in mind. However when you say safety , it is a very broad term. Let us talk about safety in terms of food. PLA is a bio degradable plastic. It is used in some medical implants which dissolve over a period of time. So it is safe for things which can hold food. But not for hot food and most of the times it is not dishwasher safe too as they tend to heat up to sterilize, which can spoil the print for you. Hence each type of filament can discussed in terms of safety according to situation.
The best filament one would recommend for dolls would be ABS since it is a little harder and not as brittle as PLA
Lastly regarding price and availability of colours, there is no difference in terms of colours between types of plastics and price depends largely on the grade and make of plastic and less on type of plastic.