why does water appear colourless whereas atmosphere is blue in colour?
Dear Student!
Sky appears blue because of scattering of light by small particles in the Earth's atmosphere. Blue colour is the most scattered colour on account of low wavelength, while other colours reaches to you with zero or very less scattering. Thus, sky appears blue.
Water which is commonly available has no colour so it appears colourless. But most of the times sea/ocean water appear blue because it absorbs colour other than blue. So, it is incorrect to say that "water appears colourless".
Hope it is clear!
Best wishes!!