Disclaimer - I am not an expert. I've had them growing in my garden for 20 years but only recently started getting interested in growing from seed or some of the non-hybrid varieties.

My understanding is that the color can be determined by the color of the BERRY that appear on the stalk after the blooms have fallen and have from 1 to 20 seeds in each berry. Once the seeds are extracted, you can't tell what color the berry was by looking at the seed. The berries take several months to ripen. My berries have all been bright red and my plants bright orange.

I've never heard of a way to predict color by looking at the plant alone.

As to yellow clivia, I found this recipe -- if things weren't confusing enough!

Yellow Clivia Genetics

thanks - it is complicated!
To take number 6 in the article, ''If a seedling is unpigmented, the only possible flower results can be yellows, creams, pastels, pinks or peaches.'' Does 'pigmented' refer to the 'sheath' I talked about in my first post?
Joe