Why is O2 (Oxygen) colorless and odorless while O3 (Ozone) is a pale blue gas with a distinctively pungent smell?
Our perception of colour and smell involve different chemistry so there is no reason why they should be related. For example, what ever the chemistry of smell is (and its not certain what this is) it clearly does not involving photons and subsequent isomerisation of a rhodopsin. 

Ozone is slightly coloured as it has two low lying electronically excited states (Chappius bands 550 to 600 nm) and a second state (at approx 700 to 1000 nm) both of whose energy gaps from the ground state correspond to a wavelength in the visible spectrum. The combined absorption is rather broad, weak and peaks at approx 600 nm which in the red part of the spectrum, thus ozone appears blue. Oxygen also has two low lying electronic states at around 700 nm and 12000 nm but are very weak and the longer wavelength transition is beyond the range of our eyes to detect it (liquid oxygen appears blue as does liquid ozone). Both O$_2$ and O$_3$ have electronic states in the ultra violet at a wavelength beyond the range of our eyes. 

( I have added a moderately detailed description as to why high pressure gas and liquid oxygen molecules are coloured. see Does O2 have a color in the gas phase )