This is the 12652nd most frequent Polish word.
niebieskich
The Polish word "niebieskich" means "blue" (genitive or accusative plural form).
In this case, 'niebieskich' stands alone as an adjectival noun referring back to a previously mentioned group.
Mówię o tych niebieskich.
I am talking about those blue ones.
In this sentence, 'niebieskich' is the plural genitive masculine or animate use, qualifying 'ptaków' (birds).
Widzę niebieskich ptaków na drzewie.
I see blue birds on the tree.
Here, 'niebieskich' describes 'płatkach' (petals), using the plural locative masculine or neuter form.