change background in ereader mode on Kindle fire

[kicker]

Hi,
I recently bought a kindle fire and would like to use it with DD who has Meares Irlen and likes to read with a purple overlay.
I know I can change the background colour to sepia or black but I need purple or other similar hue.
Would I need to download an appropriate app. I am not techie at all so need very clear instructions.
Thanks

Not something I've heard of being able to do. Certainly not an option within the official Kindle app. It's possible that one of the other e reader apps has this but they won't be kindle book format compatible and I think it's unlikely anyway as it's an unusual request.

Now I'll have to confess my ignorance as I'm afraid I don't know what Meares Irlen is, so forgive me if this is a stupid suggestion, but could you perhaps get some thin, light cellophane to lay over the screen?

I was looking at coloured gels for lighting purposes but couldn' find static clinging ones in purple.
There is PC software that you can use to change colour for people who find the white screen too glaring so I am surprised you can't find a similar solution for ereaders. How does one go about inventing an app to do this?