Since, NO has an odd electron so it is paramagnetic but its colourless? why ?
while, NO2 has odd electron too and it is paramagnetic and a browncolour gas.

Dear Student,
NO is generally paramagnetic yet it tends to frame diamers. In diamerisation, two particles with odd electrons consolidate to frame a steady structure. Since NO typically exists as a diamer, it ends up noticeably diamagnetic and thus is drab. 

 

Vikas, brother
NO doesnt undergoes dimerization, its NO₂ which form N₂O₄ at dimer stage and lose its odd electron so colourless and diamagnetic whicle its monomer NO₂ have odd electron so paramag and brown coloured. My question is about NO not about NO_2.