The sinamay on this headpiece was sprayed with motor vehicle spray paint. In fact it had 4-6 coats on it as the first colour dried a little too purple. I didn't have any problems with the weave clogging with the paint. I have learnt that you start to spray before you hit the fabric so that first blob goes onto the paper.
I use Jacquard Acid dyes all the time on parisisal capelines and hoods ( I buy them in natural in bigger quantities and a friend brings them on the plane, so I save on shipping fees). I also dye over colored sinamay at times to match a shade if needed. Never had a problem with the dyes, easy to use and mix.
the other coloring agent I would not be without is Design master sprays.....life savers!!!
I have never thought of using car paint! Does this make the hat stiffer than normal? I may need to experiment. I know I have some tractor spray on hand. I wonder how popular John Deere Green, or Allis Chalmers orange would be. LOL
Oh please don't ever use paints and sprays for cars. They are toxic! They are not meant to be used in products such as hats that are worn close to skin and eyes. They can cause an allergist reacción. A manufacturer should always pay attention to the safety of the product and think about the end user.
You are probably correct about the vehicle paint. I was so excited a few years ago to discover a colouring system developed by a silk painter here in Australia that is non toxic. She was aware of impact of dyes and paints on her health. I experimented with it in millinery and works well on fabric and all straws. This Cream Pari and cream silk was transformed using this colouring system. Her product has a combo of properties of a paint and a dye. Great to use knowing no reactions. Tinting Millinery Course listed under Headwear Trims