Xlsx Better Support Needed for Scheme/Theme Colors

[oleibman]

This is:

- [x] a bug report
- [ ] a feature request
- [ ] **not** a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

Theme/scheme colors should be read as part of Xlsx Reader, and reproduced by Xlsx Writer.

What is the current behavior?

Reader appears to ignore scheme colors. Writer appears to write theme file with hard-coded colors. As a result, the input and output files may differ in their coloring when scheme colors are used. This is especially noticeable in some charts (see PR #3476); I suspect, but am not certain, that other situations might also be affected.

What are the steps to reproduce?

Please provide a Minimal, Complete, and Verifiable example of code that exhibits the issue without relying on an external Excel file or a web server:

After the PR identified above is merged, this behavior is demonstrated by sample 32readwriteLineChart6.

What features do you think are causing the issue

• Reader
• Writer
• Styles
• Data Validations
• Formula Calculations
• Charts
• AutoFilter
• Form Elements

Does an issue affect all spreadsheet file formats? If not, which formats are affected?

This is probably just a problem for Xlsx.

Which versions of PhpSpreadsheet and PHP are affected?

All.