Both the straw color of the Luger triggers and other parts as well as the brilliant blue color found on the Colt screws can easily be duplicated with nitre salts blueing. I use the salts from Brownells and have duplicated the colors you describe many times. They come with a temperature chart that varys from the one above, but functions the same way. You simply melt the salts in the appropriate vessel, I use the "1/4 tank" from Brownells, bring the melted salts to the right temperature using a blueing thermometer, immerse the polished parts and watch for the color change. A very simple process that works well for small parts.
