You can change themes which will changes colors. Then to customize your color more click the field(s) and then you go to inspector. (you were on the right track). Click the apperance tab on the top of the inspector. The Normal state changes the color / text in normal view. Change to In Focus to change the color when you are clicked into the field. You can also change the colors / fonts when the mouse hovers over the field. Then you change the fill color and or the text color. There are several items you can change.
If you are going to select a number of different themes as an experiment to see how your layouts look, I recommend that you do so with a copy of your file that you then discard when through experimenting. Once you know what theme you like, open the copy you plan to keep and make a single theme change on any layout you want to change.
Repeatedly selecting different themes adds "stuff" to your file that cannot be removed in FileMaker 12 and your file will increase in size with each theme change.
I do not want to change themes. And from your post it sounds like experimenting with themes is poorly designed as it leaves junk stuff in your file. The theme I am using started off as one of the stock themes with FM9 that I heavily modified to my preferences. It used to be in the theme list when I created new layouts, but just noticed it is no longer in the list as I have not created a new layout since I upgraded a couple weeks ago. My program is an ever evolving creature with more than a hundred layouts in it and 60 tables with a relationship chart that takes 30 pages to print.
to re-itterate the problem: Apparently when I converted from FM9 to FM12, the color used for a field with all contents selected was changed to a lighter gray which is too close to the light grey of the normal field so it is not obviously perceptable that the field is selected. I do not like ANY of the canned themes. I simply want to make the color used that shows selected contents to be darker.
A quick count across my layouts shows about a thousand fields across a hundred layouts that I would have to manually correct. It is ridiculuous that I would have to manually correct every field in every layout manually. What I want to do is use my current theme, simply change the color value used for selected contents and apply that change across every layout. All layouts use the exact same theme.
I just noticed that my theme that I created does not appear in the theme list when I am creating a new layout. How do I get it into the list? Or another way to fix this would be to modify one layout then save its theme as a template that gets added to the system for future use and simply convert ALL layouts at one time to my customized theme. How do I do that?
You can select several fields at one time on the current layout and changes colors, which is still very take a long of time and you would still have the problem of duplicating your current custom theme.
There is a work around that you can use to create themes. See the following post.
There is not a good way to keep your old theme. Sorry.