Here you go...

https://www.hunker.com/13411341/what-type-of-paint-will-cover-a-plastic-picture-frame

Chalk paint will cover a plastic frame. I would give it 2 coats and use a clear poly to seal it--a water based polyacrylic. Here's a pretty one for some info!

https://www.lovelyetc.com/how-to-transform-a-plastic-picture-frame

Krylon makes a paint specifically for plastic. I would use a primer then spray paint the frame whatever color you like.

A spray paint meant for plastic would make quick work of repainting.

This post might help

https://www.hometalk.com/29021448/turn-1-picture-frames-gorgeous

Turn $1 Picture Frames Gorgeous!

Chalk paint works great as does spray paint and then I like to shabby them up with some darker glaze or even dark brown English Furniture Polish works really good. Or even just sanding them. Yes even on plastic.

Rita: Simple, all-purpose spray paint will work

I would take the mirror out of the frame if possible first. Than sand and wipe it down. After it dries just use some cheap old color place (walmart brand) spray paint. Remember several light coats are MUCH better then a few heavy coats. You don't want any runs on the mirror.

Hello. Spray paint or chalk paint?

Considering chalk paint, I might suggest to have a look at this blogger transformation projects and see if her aesthetic and color choices may appeal to you.

https://www.confessionsofaserialdiyer.com/diy-gallery/

Hi Rita. I would remove the frame from the mirror if possible. Sand the frame and wipe it down. Use the spray paint made especially to cover plastic. Give it a couple coats of paint and then return the mirror to the frame.

Spray paint would work best. You can wither cover the mirror and spray paint the frame or remove it if posssibe.

Rough with fine steel wool, clean with denatured alcohol, them spray paint with Krylon which is formulated for plastic. Make sure to tape off the mirror and cover with paper to prevent overspray.

Here's a post that might help - https://www.thesprucecrafts.com/paint-a-non-removable-mirror-frame-2879020

Tape off the mirror and spray paint it

I've done this. I used painters tape and taped around the middle of the mirror and you can also cover the mirror part and then spray paint the plastic.

I used chalked paint and or spray paint. Either tape the glass or remove it if possible. I used chalk paint that I made my self as I like it a little thicker. Then when dry sanded all of the areas that stuck out so that when I glazed it it would give it that antique look. I also made my own glaze or used dark Old English Furniture Polish.

Spray paint works like a charm.

Chalk paint is great for this. This is my chalk paint of choice: https://bachelorettepadflip.com/2016/09/28/my-chalk-paint-of-choice/

Fortunately there are paints for plastics now. Here are several options.