I hesitate to say "a quilting principle", as that sounds like a rule. And as we all know there are no rules and no quilt police. I guess it would be better to say a "quilting guideline". This guideline has always worked well for me in the past, but it has been so long since I thought about it that I completely forgot about it.
"In a scrappy pieced quilt, one should have about 20% maverick blocks, and no more than 25%. A maverick block is one where the color arrangement is different, or pieces are turned differently, or a non-theme color is included, or low contrast fabrics are used. Maverick blocks bring interest to a quilt and cause the viewer to look more closely at what is going on".
If I remember rightly I learned this from Darra Duffy Williamson when I took a scrap quilting class from her in Houston in the fall of 1992. After class I spent a lot of time examining photos of scrappy quilts I loved, and the best always included about 20% maverick blocks.
That explains what bothered me about "Hat Trick". I'd made 11 blocks, and 5 qualified as low-contrast maverick blocks. That was WAY TOO MANY for the number of blocks I had and the pattern was getting "lost". So this evening I made 10 more blocks, all with high contrast. I made sure to balance the number of brown, green, and red blocks. The greens were all mediums, so I used the lightest contrasting fabrics I had with the greens.
Once I finished I started playing with them on the design wall. What a difference it made! 20 blocks, with either 4 or 5 "mavericks". I've still not settled on a final block arrangement, including which block to leave out, as I still haven't found an arrangement that says "this is it". So I'm going to play with them through the weekend, taking pictures of each arrangement. I've no arrangement has "spoken" to me by Monday I'm just going to pick one and sew it together.
A huge thank you for all of you who gave me suggestions - they really helped me not give up. As it turned out I didn't add any fabrics - I just made better use of the ones I had. I know I'll be happy with the quilt, no matter what arrangement I eventually choose.
Each picture is different from the others, with a change or one or
more blocks and/or alternate squares. If I'd not changed the placement
myself I, too, would think at least two or more of them must be the
same. And I'm not ruling out the idea of making a couple more blocks
either, so I have more to choose from.