Trying to increase my party pets (eclipse and Valla ) when I will come across a creature like for example a uncommon Vulnyx I I have noticed that there are coloured stars like for example white and green

What dose that mean? And why are they different colours and different numbers of stars please can someone tell me?

The number of stars indicate the difficulty level of an encounter, the more star there are the more powerfull your opponant will be.

For wild pets, the color of the star indicate how many trait points (tp) they have :

white (common) = 0
green (uncommon) = 1
blue (rare) = 2
purple (epic) = 4
yellow (legendary) = 6
red (mythical) = 8

It take 2 tp to make a visible trait so unless it is a mythical rarity pet you may not be able to see the trait(s) until the pet is tested. For others enemys or non-catcheable pets related to the story lignes (bosses) the star is white by default.

Thank you so much it means a lot now i know to look out for purple-Yellow and red pets

to clarify a bit further on the exact numbers:
white = 0tp (nothing)
green = 1tp (one carry)
blue = 2 (two carries, or one vis)
purple = 4 (4c, or 1v2c, or 2v)
yellow = 6 (6c, or 1v4c, or 2v2c, or 3v)
red = 8 (2v4c, or 3v2c, or 4v)

full breakdown, including number of stars and LG bonus stat correlations here