I am in the process of replacing the dash on my 1995 VSPEC which of course has the tan interior. The new (?) replacement that I have got hold of is standard black. I can transplant all the tan items eg bumpers, glovebox etc but that leaves the 2 side panels above the footwell.
I have found that the Miata boards recommend a SEM duplicolor CAMEL no 15173 vinyl & fabric colour rattle can. But it’s in USA and cannot be sent overseas. So
Try your friendly local auto factors or body shop. Saw a sign in a local Motosave saying they mix thousands of colours. Should be able to do a rattle can suitable for painting plastic bumpers which should do the job. Scan the colour from an existing part such as the glove box lid.