These seem so fun!
I think they look fine and you've done great with the pattern, but can see what you mean by them maybe not 'standing out' enough. And when looking at the placemat photo, yes, the J's do get a little lost, not terrible, but I can see that they may not be what you were hoping for. Of the ones you have posted, I like the H's the best, so think it may be as simple as choosing the colors/fabrics a little differently. Going with a light or bright fabric for the letters and a darker or deeper color for the background gives it a lot more contrast and then the letters really jump out at you. I also think that using patterned fabric for the letters and solids for the backgrounds help so stick with that. If I get any more ideas to help after it's mulled over in my brain a bit, I'll come back to post.
What about flipping the fabric so the letters are solids on a print background? I think they look fine too but that is an option.
It's mostly the last photo that I don't like, where I'm actually making the one into a place mat. I would love for it to work that the letters can be in the print fabric, just not sure how to accomplish it when adding into the letters to bring them to size.
I've been thinking about this. I think the placemat is fun the way it is but if you want the letters to stand out more what if you add some dense quilting in the solid color surrounding them?
Gorgeous. I can see what you mean about the J not standing out. Possibly just colour choice with the colours being the same tonally. If you are up to pulling it our you could change the orange to something slightly lighter. Or pull a colour from the other side of the colour spectrum. Possibly heavy quilting as Rebecca suggested would make the J's pop a little more, if you don't want to start again.
I agree - i think the letters look great but I see what you mean about the J's not 'popping'. You might try fabrics with more contrast next time around... the J's are both warm colors and close to the same tone (that's not the right word but I don't know what the traditional quilters' word for that is)... If you took pics of your fabric choices using a digital camera, then switch it to black and white -- then choose fabrics that are contrasting (from the b&w pic... for instance have the letter be a "white" from the b&w pic and the outside be a "black). hope that helps... but either way they're looking great!