There is a significant difference between red and blue paint. Red paint is made with the pigment called cadmium sulfide, while blue paint is made with the pigment ultramarine. These two pigments have different chemical compositions and react differently to light, resulting in different colors.
Red paint appears red because it absorbs all colors of light except red, which it reflects back to our eyes. Blue paint appears blue for the same reason - it absorbs all colors of light except blue, which it reflects back.
When mixed together, these two pigments can create a wide range of colors, from purple to green. However, when mixed in equal parts, they will cancel each other out and create a gray color.