In the USA indoor and outdoor signage, safety signs and architectural signs are required to be accessible for those with visual impairments. The difference in contrast between the support base used and the colors used must be at least 70%.
Use two pieces of plastic in contrasting colors. ADA signage mandates high contrast colors for the visually impaired, but does not give specifics of what is and isn't compliant, and your software won't tell you what combinations are
Use Gravotac - a single layered material, available in 3 thicknesses and a variety of colors for interior or exterior use. Profile material is available with or without adhesive backing. This material is also great for UV printing, hot stamping and screen printing.