Let's unpack that a bit.
You received specific feedback that you need to tone things down a bit to give a co-worker a chance to ask questions and express his opinions.
You're interpreting this to mean that you need to change your personality to suit others. Is your assumption correct, though?
It seems to me that you're being asked to give equal space or airtime to a coworker so that they can also make a contribution to the discussion. Now your coworker may be less talkative, or less forceful, or any number of things.
Fact is, your senior designer wants you to share the stage. That's very different to suppressing your personality. All it means is that you need to talk less. And when you do talk, make it count for more! So it's not about changing your personality but about moderating certain behaviours at times, for the benefit of all.
If you see this as an opportunity to draw your coworker into discussions, to ask for his perspective, and wait for him to make a contribution first at times, you'll be meeting the expectations of your senior designer in no time.
You may enjoy reading my blog about feedback on our main website: Is feedback your enemy or your friend. Feedback is a gift - because it allows us to see things through a different set of lenses. Often small tweaks to our behaviour bring massive benefits. We just have to remind ourselves of this!