Mary, very pretty. I have seeds sown now for some yellows the breeder told me were nice, it's going to be a couple of years before I know for sure.

I have just one true yellow in my garden, Heronswood Yellow purchased as a plant...it's really stingy with seed set. Lots of flowers but very little seed produced and the plant is several years established.

Try selfing it with controlled hand pollination to see if you get more seeds perhaps also producing seedlings with even more yellow flowers.

Don't know how many generations of these can be selfed before genetic stagnation, partial or complete sterility or similar problem might set in - perhaps you are seeing some of that with your plant. Suspect the strain is derived from only a comparatively short term of selfing, but don't know.