Anchors Spooner’s colour puzzle (9)

I believe the answer is:

mainstays

I'm a little stuck... Click here to teach me more about this clue!

'anchors' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Perhaps there's a link between them I don't understand?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Another definition for mainstays that I've seen is " guys".)

I've seen this clue in the Sydney Morning Herald.

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