The dark curtains have better shading performance. Such as burgundy dark purple and so on.

Second, it depends on the material of the curtain. There is a curtain that is thin and the stitches are very thin. Even if the curtains are dark in color, they are transparent.

To  put  it  simply, darker curtains are more densely shaded, and the shading effect is definitely  good.

If you particularly value shading, there is now a "shading cloth" on the back of the curtains with  a layer of woven silk with very dense stitches. Can greatly enhance the shading effect of curtains. What color and material are there?  Generally hotels are golden woven silk.

"Shading cloth" is not expensive or cheap, it is similar to gauze curtain, you can consider it as appropriate.