What version of Filemaker are you using?
Is this a nonchanging color that you want to select? (make the first tab red, the second green, the third yellow...)
Or do you want to see one color when the tab panel is selected and a different color when it is not?
I am using Filemaker 11. My highlighted areas are light grey and non-highlighted dark grey. I would like to change the whole colour theme to say, blue, but I cannot for the life of me see how to change the non-highlighted areas.
I want to see for example, light blue when the tab is highlighted and dark blue when it is not. The tab would not be changing otherwise.
Apologies, but it's still not clear to me what you mean by the "non highlighted areas".
In your screen shot, do you want the panel's fill color to change from grey to another color such as "blue"? Do you want the fields to turn blue? OR ?
I don't know of an easy way to make the tab panel change color in FileMaker 11. 12 offers some additional options not available in 11 that might serve but that's not a solution you can use here without upgrading... (A "tab panel" is the part of the tab control that pops to the front when you click on an individual tab. Your example shows 6 tab panels in your tab control.)
You might be able to carefully locate a Text block with just a single space in it, sized to fill the entire tab panel and located behind the other objects in the tab panel. It could be conditionally formatted to change fill color when a field or global variable's value is set to a specific value. Then a script triggered by an OnObjectModify trigger could use getLayoutObjectAttribute to determine if the panel containing the text block is the front panel and set the value of this variable or field to make it change color.
By 'non-highlighted areas' I mean the tab panels which are not clicked and 'active'. It seems that changing the fill from dark grey to another colour is not possible currently in FM11 unless a scripted text block is created.
FM12 seems to have some good design features. Shame not possible in 11.