Mandomemory, first off WELCOME to TDH! :cheers
This will explain Galactic's reference.
I agree that about any type of compression clothing, or snug fitting clothing would probably work. As a general rule, synthetics don't dye nearly as well as natural fabrics like cotton, wool and silk. I'm not sure if this would suit your needs, but you may want to consider cuddlduds or something similar.
http://www.cuddlduds.com/warmunderwear/
Whether or not it is dyeable depends on the fabric. The Coolmax will
not take a dye. The silkwear is 100% silk and
can be dyed. There is also some 100% cotton that would dye easily. I'm pretty sure this stuff is less expensive than Under Armour.
It's good to see more women getting into this hobby
and if you are doing a custom Mandalorian, you have A LOT of creative license. The best guidelines would be your custom Mando should look like she just stepped out of a Star Wars film. Browse the custom sections for ideas. A lot of them are awesome! Just post a concept drawing or something and get some feedback on it.
Keep your goal in mind and post any time. 98% of the people on this forum are very cool and very helpful. Remember the Search function is your friend.