For a research project I decided to create color chart image .png files (attached) in MS Paint (I will describe later why) of various acrylic paint manufacturers, including Vallejo, old Polly Scale, Tru-Color, Tamiya, Testors (includes Model Masters), Golden, RAL (never heard of these) Revell, Humbrol, and most importantly IMHO, the Federal Standard Color Database.
These colors were snipped from a datatbase at the following location (this site is interesting in itself!):http://scalemodeldb.com/paintcharts/federalstandard
The Federal Color Standard Database can be found here:http://www.fed-std-595.com/FS-595-Paint-Spec.html
The reason I created these in MS Paint is because one can copy/paste from there to another MS Paint file with a transparent background selection (white in MS Paint) to overlay an image color you are trying to match.
Each file has one or more white stripes through the various color swatches in each file to help in the overlay, essentially you want the color to disappear when overlaying onto the color you are trying to match.
1) Open desired image of the color you are trying to match in MS Paint
2) Open a the .png file of a given brand in MS Paint
3) Make sure "Transparent Selection" is checked in the Select pull-down)
4) Window-select all or a portion of the chosen swatch and select Copy
4) Go to your original image and paste the selection
5) Move the pasted image around on your color and look to see how close you can get- again the goal is to maker the pasted color disappear into your desired color.
There may be other ways to do this, but I am not versed in those applications, I use MS Paint every day.
You may never get a perfect match, but you may come very close.
Here is an example, my best match is difficult to see down at the bottom right of the siding on the building:
NOTE: this DOES NOT resolve actual paint color issues from the bottle.
I found this very helpful in my project to at least make an educated guess about a color before buying hundreds of paint bottles, and thought it might be helpful to folks here too.