Color profile in browsers

CSS background (128,0,0 pixels)
Canvas (128,0,0 pixels)
PNG (128,0,0 pixels) with no ICC Profile
PNG (128,0,0 pixels) with sRGB profile
Canvas -> dynamic sRGB PNG
CSS background (sRGB translation with JS)

CSS Color Module Level 3:

All RGB colors are specified in the sRGB color space (see [SRGB]). User agents may vary in the fidelity with which they represent these colors, but using sRGB provides an unambiguous and objectively measurable definition of what the color should be, which can be related to international standards (see [COLORIMETRY]).