## Why is this an issue?

Shared coding conventions allow teams to collaborate effectively. Writing colors in upper case makes them stand out at such, thereby making the code easier to read.

This rule checks that hexadecimal color definitions are written in upper case.

### Noncompliant code example

    $white = '#ffffff';  // Noncompliant
    $dkgray = '#006400';
    $aqua = '#00ffff';  // Noncompliant

### Compliant solution

    $white = '#FFFFFF';  // Compliant
    $dkgray = '#006400';
    $aqua = '#00FFFF';  // Compliant