Is it OK to paint on Lafarge span flex roofing underlay with emulsion paint?

Question

I wish to lighten a loft storage space by painting over an existing black underlay with white emulsion paint. Concerned that paint will reduce weather proof props of underlay

Answer 1

I have done this in the past on an industrial unit in the UK with no adverse affects.
I would still do a small test area and leave it for a few weeks to test any possible reaction with your chosen paint.
Better safe than sorry

Answer 2

If it's the underside then it'll be fine.
Why not fit boards first then paint that.