This is the 12638th most frequent Polish word.
neonowych
"Neonowych" means "neon" or "related to neon" (plural or adjectival form in Polish).
The word 'neonowych' here modifies 'instalacji' indicating the material or style of the installations, i.e., made of neon.
Oglądaliśmy wystawę sztuki nowoczesnej z neonowych instalacji.
We were viewing a modern art exhibit featuring neon installations.
In this sentence, 'neonowych' is describing 'szyldów', specifying the type of signs; specifically, they are made of neon lights.
Na ulicach miasta widać dużo neonowych szyldów.
There are many neon signs visible on the city streets.
Here, 'neonowych' characterizes 'kolorach' referring to the bright and vivid qualities of the colors.