I have seen several wood lilies in the Rocky mountain parks but this is the first and only yellow variant I have come across. It was surrounded by the more typical rust coloured form. Unfortunately these plants are becoming more rare as people continue to try to transplant them, with little success, to their gardens.
Owen Slater Photography 
I found one this year too. Near Nordegg. I’ve been searching for more info and came across your site. Too cool.
Neat…they remain rare because unfortunately they get picked before going to seed.