How to change colour of hyperlink in Numbers
This is actually not a question, but an answer. After having tried in vain to find out how to get linked text in Numbers automatically underlined AND coloured blue, the way this happens automatically in most software, I decided to see if there was a solution in Pages, which is so similar in basic design. And I found it!
This reply from VikingOSX in 2019 applies just as well to Numbers:
Select the existing link content. Then ⌘-T to open the Font panel. On its toolbar, locate the underline category, and select Color. Change the color to your desired link color. The selected link in the document will now be that color. In the Character Style menu, pass your pointer over the right side of the existing Link style. The Redefine from Selection will be selectable, and click that.
Your modified link color will only survive in the current document. You will have to save a document with this modified link content as a Template from the Pages file menu, and subsequently, you would choose that template when you want revised link color in future documents.
Parallels, macOS 10.14