It's colourful and huge, but not grand (3)
I believe the answer is:
hue
'it's colourful' is the definition.
I can't tell whether this defines the answer.
'huge but not grand' is the wordplay.
'but not' indicates named letters should be taken away.
'grand' becomes 'g' (G is short for grand as in a thousand).
'huge' with 'g' taken away is 'HUE'.
'and' is the link.
Can you help me to learn more?
(Other definitions for hue that I've seen before include "red or black, say" , "Tone, shade" , "General hubbub - . . . and cry" , "'Pigment, colour (3)'" , "Shade of colour; Vietnam port" .)