I'm not seeing how changing the color of the coping is going to make it "blend" better with the deck. It's already a dead ringer color that matches the deck. Did you mean contrast with, or otherwise frame the deck? Personally, I don't like that red brick look, or the coping color. Both seem very dated to me. More pics of the house and yard would help you to get better advice about a color scheme. That is if you want the pool to look a part of the entire landscape. Start there.
And/or discuss the overall theme you're trying to achieve. Many love that brick look. Others freshen their yard with modern grays or other neutrals (red is not a neutral color). What else is in view of the pool that can be used as key colors? That might influence a choice for edge tile or coping color. Does the owner like monotone themes (tints and shades of the same colors) that imbue tranquility? Or contrasting colors that create a bold look? Subued colors, or bright colors?
I've called in my guru who knows all there is to know about altering the color of tile and brick. He can give us his thoughts about what is possible. But he'll also need a sense of the rest of the surrounding materials (fence color, house color, etc) to advise about specific colors.
As Kim points out, the darker you go with the finish, the more mottling you're likely to get. My previous dark finish was very starkly mottled. My new finish hasn't started mottling yet. Another here has a brand new dark finish that was "born" mottled. So it's a risk. I personally don't mind it, it's just looks "organic" to me, the variations of the color. But if you're looking for a pure, solid, perfect dark color, you have to face the possibility of being disappointed, at first or in the future as it ages.
Right now, the blue-green of the pool, the bright blue of the tile and brick red are fighting tooth and nail with each other. So you're on the right track, in seeking the fix. Post pics of the surrounding yard and of the house. Fill us in on the type of colors that the owner likes. And we'll go from there.
I didn't design my pool. The previous homeowners did. But I love it. It is considered dark, but it's not black. It turns a lighter shade depending on the time of day. My edge tile is river rock, which I love. It supports the color of the pool finish, and it matches river rock pathways that decorate my landscaping, which tie together my yard and pool. The deck is a contrasting color to the water, but the turquoise and tan are harmonious and organic (not artificial like some pool color schemes look like to me).
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