Methinks you need a bit of mechanical engineering design Joe. Like struts/cross-bracing where the tipped-back chair and posterior are aiming for. Add wood IMNSHO.

Colours you say? Is red available? Red does absorb all wavelengths except red. But it must be somewhat translucent for the UV to penetrate.

I must have! Er - maybe not at this price Dymax Ultr-Red 3113-UR