You sound like you're more than a capable cook in the kitchen, so try not to beat yourself up. We all have our off days, Smilingcat. In fact, I can't count how many times you've had me drooling. No worries or need to fire yourself. Maybe it's time for a short cooking break?
The mushrooms in the sauce sound like a nice addition. How about giving the mushrooms a quick saute and adding them to the sauce after it's done next time? I agree that blue cheese gives the sauce more depth, but I still have added powered mustard and paprika or ceyenne with it. Maybe I'll try leaving it out next time. And I never thought about using gruyere. I usually use Colby or Monterrey Jack cheese for the creamy consistency. I'll have to try it, though: it sounds good.
Also, forget about the orange color. I do use cheddar, usually aged extra sharp, for the flavor and tang it adds, but I get the kind with no added food coloring. It takes a while for people to get used to, especially if they've been raised on the boxed stuff (Don't get me wrong, with kids and the convenience factor, I still keep some in the house.
) ; but the taste more than makes up for it.
Everything in moderation, including moderation.
2007 Rodriguez Adventure/B72
2009 Masi Soulville Mixte/B18
1997 Trek 820 Step-thru Xtracycle/B17