How Do You Change the Brick Color?

I already did BrickColor = New Yeller

You need to use the BrickColor.new constructor.

local part = game.Workspace.Part1 --Referencing the part you want to change color.

part.BrickColor = BrickColor.new("New Yeller")

You can use part.BrickColor for ordinary color names (blue, red, green, black, etc.)

local part = game.Workspace.Part1
 
part.BrickColor = BrickColor.new("Green") -- Color name

Or, you could use part.Color3 for more variety. Note: You will have to use Red, Green, and Blue values with Color3, not color names!

local part = game.Workspace.Part1
 
part.Color3 = Color3.new(255, 0, 0) -- Red, Green, Blue values

I hope this helps, good luck!