This is one of those cases where a picture is worth a thousand words. Al

Yes, always post a pic if you can, we love pics..

I would hold of on a repot until next spring if the mix sems to be ok to you.
When I loose color in mine it is usually because your waering mixture pH is too high over time or because of nutrient delivery problems...Sometimes not feeding enough could also impact the vibrant colors..

Another culprit could be poor root function due to a poor mix..I hope that is not it.
If it's just happening now, or recently, you also attribute cold weather to that too.

MIke

It's a Meyer, which is quite sensitive to significant changes in light conditions; if you moved it directly from outside to inside, it will drop a lot of leaves to replace them later with new leaves better suited to the new light conditions.

I wouldn't pot up until the spring personally, unless it's in a tiny pot. It's going to slow down considerably inside so I wouldn't mess with it. I'm no expert but I've found it's best to repot right before it's going to start actively growing.

That being said you don't need to bring it in just yet. I live in Massachusetts and don't bring my lemon tree in until we have consistent temps below 45F at night. Then if you're up for the extra work, I bring mine in at night and will bring it outside in the morning if the temps are above mid 40's when I leave for work.

Don't underestimate Johnmerr's advice on significant light changes for Meyers. Your tree will do better if you slowly transition it to low light over a month or so. Fully shaded outside is still more sunlight than most indoor locations. This is especially true in the spring, you'd be amazed how easy it is to sunburn a plant that's been inside all winter(which I learned from experience).