Innovative feature suggestion: Depth coloring for Ada 2012 code

Dear GPS developers!
Please add depth coloring to Ada 2012 syntax highlighting in the 2017 release of GPS.

Depth coloring makes it easier to see the nested indenting structure of code, by making minor changes to the editor background color that highlight each level of nesting.

Please see how it looks for F# code:
Light theme, Microsoft Visual Studio 2015:

Dark theme:

For referential use: The begin, end keywords and semicolons exist, but are non-mandatory in F# due to its indentation-aware syntax. In F#, whitespace - spaces and newlines - is significant. Indentation is used to indicate when statements and blocks of code are complete. Typically, a block of code is indented by four spaces, for readability purposes. The indented block of code in F# is an equivalent to a block of code inside the begin .. end keywords in Ada 2012 and F#.

Finally, I can tell you from my experience that coding with the depth colorizer is like changing an ancient Trabant for a modern Mercedes. It is a real pleasure to code with depth coloring. I believe the Ada 2012 language users would love this feature in the next release of GPS.

The issue requests depth coloring for Ada 2012 syntax highlighting in GPS and links to light and dark theme examples. No files, tests, or entry points are named; first review the existing editor syntax-highlighting and indentation behavior, then clarify the implementation scope and validation criteria with maintainers.