How do i fix this script on changing block colors?

Please use a code block in the future

With using a code block, your code looks like this,

local Part1 = game.Workspace.FancyJumpParts.Part1 
local Block1 = game.Workspace.JumpBlocks.Block1

while true do 
    Block1.BrickColor = BrickColor.Green() 
    wait(3) 
    Block1.BrickColor = BrickColor.Yellow() 
    wait(3) 
    Block1.BrickColor = BrickColor.Black() 
    wait(3) 
    Block1.BrickColor = BrickColor.Random() 
    wait(3) 
end

while true do 
    Part1.BrickColor = BrickColor.Red() 
    Part1.CanCollide = false 
    wait(5)
    Part1.BrickColor = BrickColor.Blue() 
    Part1.CanCollide = true 
    wait(5)
end

The problem,

Lua can only do one thing at a time, and it reads from top to bottom, mainly. Once the code reaches the first loop, it never sees the other one. It never breaks out.

There are multiple ways of fixing this, but since you want specific timings, I would suggest the simplest solution by using the spawn function.

This will allow your code to see both loops and deal with them accordingly.

local Part1 = game.Workspace.FancyJumpParts.Part1 
local Block1 = game.Workspace.JumpBlocks.Block1

spawn(function()
    while true do
        Block1.BrickColor = BrickColor.Green() 
        wait(3) 
        Block1.BrickColor = BrickColor.Yellow() 
        wait(3) 
        Block1.BrickColor = BrickColor.Black() 
        wait(3) 
        Block1.BrickColor = BrickColor.Random() 
        wait(3) 
    end
end)

while true do 
    Part1.BrickColor = BrickColor.Red() 
    Part1.CanCollide = false 
    wait(5)
    Part1.BrickColor = BrickColor.Blue() 
    Part1.CanCollide = true 
    wait(5)
end

Good Luck!

If I helped, please don't forget to accept my answer.