Workspace.Script:2: 'then' expected near '=' <== Why is this??

if game.Workspace.Part1.Transperence == 1 then -- the error is the u use only 1 =.  == means is same as ~= means different as. and >= bigger and same. > only bigger as. <= smaller and same >only smaller as.

    game.Workspace.Part2.Color = BrickColor.DarkGreen()

end

Your first problem: you're using = rather than == in the first line. When you check something, you use ==, and when you define a variable, you use =. Your second problem: you're setting the part's Color when you should be setting its BrickColor.

Fixed version:

if game.Workspace.Part1.Transparency == 1 then
    game.Workspace.Part2.BrickColor = BrickColor.new("Dark green")
end

Also, a tip: use workspace rather than game.Workspace. Just makes things a bit easier.

You have to have two ==s because it signifies that the transparency is equal to 1. Also here's a re-written code if you want it

if game.Workspace.Part1.Transparency == 1 then
    game.Workspace.Part2.BrickColor = BrickColor.Green()
end

Remember; you always need a double "equals" after an "if" or an "until" statement.

if game.workspace.part1.Transparency == 1 then
    game.workspace.part2.BrickColor = BrickColor.Green()
end

The way I remember it is to do a peace sign. You lift up your middle finger and your index finger. These two fingers mean the two "equals" you need to add in there.