Plastic sheathing and masking tape was not available at the end of the painting project for whatever reason, I have no idea, but you have a Paint Brush that if not cared for will eventually dry up. Last solution that works well, is to take a sopping wet rag, wrapping the Paint Brush up like that burrito you missed wrapping up earlier. This will buy you some time until either you use the paint brush again, or you can properly clean it.
Like this, it will actually take quite a while to reach a number that is close enough to the yellow color you've chosen that you can't tell any difference (and mathematically, you will never actually reach an average of 4!)
If paints have been allowed to stand and hard lumps or skin have formed, the skin or scum should be removed, after which the paint can be stirred and strained through screen wire or through one or two thicknesses of cheesecloth.
At a minimum you want to remove all the chrome from the car. Take off both front and rear bumpers. If your Mustang has bumperettes that are body color be sure to bring them along so they can get sprayed at the same time as the rest of the car. Remove all rocker, hood and trunk molding. Same for wheel well molding and all emblems. This would be a good time to order some new emblems and attachment hardware. Also spend some time cleaning up all the chrome with #0000 steel wool. Nothing looks worse on a fresh paint job then faded emblems and corroded, cloudy chrome.
Mixing. Paste paints, such as aluminum, resin-emulsion, and lead-in-oil, should be stirred with a stiff paddle and reduced to painting consistency with the liquids recommended on the manufacturer's labels.
The stencil must be held very firmly against the surface with one hand, and the stencil brush worked over it quickly with the other hand. Or, if you have an assistant, it is best for one person to keep the stencil steady, while the other does the painting. In removing the stencil, make sure you pick it up without smudging.
White - is the concentration of all colors from the physical standpoint, since it is the white light that decomposes into all the colors of the spectrum when refracted in the facets of the glass pyramid. White color goes well with all the other colors, it is universal and brings in the element of elegance.