I have not infused goldenrod flowers in oil, but a quick Google check for pics of oil infusions others have made shows this infusion is often a green-yellow. And a quick Google check for soap made with goldenrod infused oil resulted in a pic of a tan colored bar -- definitely not yellow.
You say this is your first infusion and you want yellow. I suspect the silence regarding your questions about goldenrod is that it's not something many people use for a colorant in soap. Why not try a botanical that has a proven track record? If you want a yellow botanical for soaping, I'd focus on something like calendula, turmeric, annatto, or ginger. More ideas: http://www.mullerslanefarm.com/soapcolors.html
If you are determined to stick with goldenrod, then do a test to see if it has some reasonable promise of working in soap. Try mixing a small sample of the infused oil with a bit of lye solution and see what happens. If the color morphs, it's not going to be a good choice for soaping, even if you were looking for a greeny yellow colorant.
You say this is your first infusion and you want yellow. I suspect the silence regarding your questions about goldenrod is that it's not something many people use for a colorant in soap. Why not try a botanical that has a proven track record? If you want a yellow botanical for soaping, I'd focus on something like calendula, turmeric, annatto, or ginger. More ideas: http://www.mullerslanefarm.com/soapcolors.html
If you are determined to stick with goldenrod, then do a test to see if it has some reasonable promise of working in soap. Try mixing a small sample of the infused oil with a bit of lye solution and see what happens. If the color morphs, it's not going to be a good choice for soaping, even if you were looking for a greeny yellow colorant.