I need help making a health = color logic equation, could someone help?

Hello, I am attempting to make a dummy change it's color according to it's health. I'm using the Color3.fromRGB system and I don't know how to do the "Red" part. What I plan is to have the Red value go up if the health goes down, and have the Green value go down if the health goes down. Here's my code.

local function CheckHealth()
    Color = Color3.fromRGB(0,2.55*Hum.Health,0)
end

I'm still stuck on the Red part, I know how to do the Green but I just can't find out what logic to use. If someone could help, it'd be great! Thanks!