It's weird seeing number two dressed in blue (6)
I believe the answer is:
spooky
'it's weird' is the definition.
(I've seen this before)
'number two dressed in blue' is the wordplay.
'number two dressed' becomes 'poo' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'blue' becomes 'sky' (I've seen this in other clues).
'poo' inserted within 'sky' is 'SPOOKY'.
'seeing' is the link.
Can you help me to learn more?
(Other definitions for spooky that I've seen before include "Rather frightening" , "Eerie" , "Chilling" , "Sinister, ghostly" , "weird" .)