Honestly, I don't think a blanket "use colour for all places in the UI" rule is correct. Unfortunately, when it comes to form fields, it's not that simple. This is referring to a field which by the HTML specification is named "color" and all of the in-code references follow that pattern versus the en-GB preferred variant.

When it comes to specifying the color of something like some template options do, I think this type of change is fine. But when it's referencing a specific field type which has a specific naming convention, IMO it might be better suited to follow that.

Says the guy from the now biggest laughing stock of a country on this planet.

AFAIR (can't remember exactly) we had the same discussion in a Tiny or JS language file end then the decison was made to follow the "colour" rule.
I will have to check "deeper" just to be sure to be consistent.

When it is in code use CSS or HTML standards, when visually presented to the user use en-GB (except when user need to enter a CSS or HTML value that need to be in that standard)

In this case, it is referring to something that controls an HTML element with a specific identifier. It is a <input type="color" /> element so IMO the correct name for anything referring directly to that HTML element should use "Color" to remain consistent with technical specifications. When referring to a color value of any type, colour or any other localised variant should be used. In these examples, they have two vastly different contexts which I believe does call for evaluating which variant is the correct one to use versus applying a blanket "en-GB all the things" rule.

See my comment here:
#13659 (comment)

Imho, if the field types get translated, then it can be colour here as it will be "Farbe" in german and "couleur" in french. So it would not be tied to the HTML element name in translations and thus also doesn't have to be in english.
If we're not going to translate them, then it has to be color as it is a reference to the input element type.

If we're not going to translate them, then it has to be color as it is a reference to the input element type.

I am in favour of not translating the field types.

I propose this:
#13659 (comment)

In that case we can use for example for this plugin

PLG_FIELDS_COLOR="Fields - Colour"
PLG_FIELDS_COLOR_LABEL="Colour (color)"
PLG_FIELDS_COLOR_XML_DESCRIPTION="This plugin lets create new fields of type 'color' in the extensions where custom fields are implemented."

Please see and test #13710