CDD-2219: Add TREND_LINE_NONE to simplified chart colours

[phill-stanley]

Description

This PR includes an update to the charts colour scheme to include a none trend line colour for charts that don't have trend data.

Fixes #CDD-2219

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Type of change

Please select the options that are relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Tech debt item (this is focused solely on addressing any relevant technical debt)

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Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests at the right levels to prove my change is effective
• I have added screenshots or screen grabs where appropriate
• I have added docstrings in the correct style (google)

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[phill-stanley]

[A-Ashiq]

If this is meant to be a dark blue, then why haven't we used the existing COLOUR_1_DARK_BLUE rgb colour? That has already been user tested and approved

[phill-stanley]

Good catch, checked with front-end and the COLOUR_1_DARK_BLUE is fine for this, will close this branch and update the alt-text branch.