Drengen læser pigens personlige lyserøde brev Why would personlige and lyserøde end in e if there is only one brev?? Is it because there is more than one adjective??

When I am telling time how do I know when to use "i" or "om"?? For days of the week or telling people what time of day it is or whatever. Like "I work on Friday" or just any random time related thing in general.

Which is more correct... "Farverne er røde og hvide" or "Farverne er rød og hvid"?? I have been using Duolingo to help me in between tutoring sessions and it wanted me to translate "The colors are red and white" into Danish. I wrote the first one because I was thinking two colors would make it plural. And even moreso since the word "farverne" itself is plural. Why did it say the second one was right?? In this context, should I be dealing with each color as individuals even though they appear together in a sentence and with a plural??

In Danish what are the grammar rules for colors?? When do you use rød, røde or rødt?? And presumably the rule applies to all colors even though I have only seen two verions of green (grøn and grønne) and white (hvid and hvidt)?? I think the røde one has to do with adjectives or something?? Just please explain all the rules. Thank you.

langzaam or langzame?? I had a quiz and I had to translate "It is a slow sheep" and "It is a slow turtle" from English to Dutch. I wrote "langzaam" for both but then afterward I thought I might have been wrong and that I should have used "langzame" for both. I got "Het is een langzaam schaap" as correct but "Het is een langzaam schildpad" was marked wrong. Why is one "langzaam" and the other "langzame"?? Also was I correct in assessing that "langzame" would have been right??