I would say that Färgstark is mostly used figuratively about a person that is very... charismatic or something like that.
Färgglad is mostly literally about something with lively and often very different colors, but need not be many.
Färgrik is mostly literally about something with many colors, but need not be as lively.
Others may have slightly different interpretation, and dictionaries are not super specific about it.
what is the difference between writing "hennes bok är färgglad" and "sin bok är färgglad"? I know that hennes refers to someone else's book and sin to her own book but I cannot make out the kontext someone would say "hennes bok är färgglad". Can you please help me with an example?
The use of "sin" requires that the sentence has a subject since it always reflects back to the subject. Therefore "Sin bok är färgglad" is incorrect. You can simply not say that.
Hennes bok är färgglad is the only correct translation.
If the sentence had a subject, you would have used "sin".
Hon läser sin färgglada bok - She is reading her (own) colorful book
"Hennes" is a possessive pronoun and normally a possessive pronoun differs between singular and plural (e.g. min hund, mina hundar), but for hennes (her), hans (his) and deras (their), it's the same.
hon = she: "Hon har en bok" (She has a book)
henne = her (object): "Vi ger henne en bok" (We give her a book)
hennes = her (possessive): "Hennes bok är färgglad" (Her book is colourful) or "Hennes böcker är färgglada" (Her books are colourful)
In this exercise, the word is not "färg" but "färgglad", which means "colorful". The word for "painted" is "målad".
If you are translating from Swedish and you jot down "I went to the store and bought a can of color", you might want to change it to "can of paint". Context!