I've noticed that some men have a fear of mixing patterns, but here's why I think the tie you have on now actually works: effective use of scale and color. Your tartan is the largest pattern you have on. I'd rank it a medium-large one, relative to what else is going on the ensemble. Your tie has the smallest pattern. I'd say it was a medium-small scale, which is small enough to contrast with the scale of the tartan, not so small as to read as a solid, large enough to discern the pattern from a distance. It uses colors from the tartan, picking up one of the overchecks as its main color, and then echoing the rest of the main colors in the medallions. When the colors relate like this, and the patterns are sufficiently different in scale, it is to my eye a pleasing contrast to a tartan.
If you think of how someone might decorate a room, you might paint the walls a grayish blue, upholster the sofa in a tartan, and add a side chair with a cushion in a contrasting color and dot pattern in a similar way.
For an absolutely sublime example of use of pattern and texture, see
one of the photos Robert posted illustrating pocket squares in use: One large check, one very small check, one medium dot pattern, and one bit of solid.
So, if you do trade ties for a solid, my advise would be to make sure you get a pocket square with a pattern.
Regards,
Rex.
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