синий it is blue голубой it is the colour of your T-shirt on the Avatar :-)

The basic colour concepts they refer to are синий="blue" and голубой="light blue". The main colour is "синий". Most colours that are "голубой", may be considered a sub-shade of "синий". СИНИЙ is a deep, earthly, material colour, the colour of the sea. ГОЛУБОЙ is a light, airy colour. The colour of the sky (though, in poetic texts "в синем небе" is a set expression), the eye colour. ГОЛУБОЙ also includes some shades between blue and green that would not be considered "синий". The word also has the meaning "a gay".

синий = blue голубой = light blue. Голубой is more light color than blue. Try to search google.

For differences of words use image search in Google !