RGB ledstrip brightness from low to high

I have a RGB ledstrip, and i want to control it with an arduino.
I do have some code, and can fade between all colors.

But that is not what i want.

What i want is:
Choose an color (orange or light blue )
It must be a color with different RGB values not only red, green or blue

I want the color orange turn on from brigthness 0 to brightness 255
But i can only do this with Red, Blue or Green.

I have searches the internet for an example code, but cannot find anything, only fading between different colors
Can somebody help me?
Or does somebody know where i can find this code

In the past i have used shiftpwm to control multiple ledstrips, that works.
But now i have only one ledstrip and no shiftregisters