Why do my TruTone bulbs look different from my old incandescents?

Your eyes are not playing tricks on you. It's a real thing and pretty much everyone who mixes filament LEDs with old incandescents notices it eventually. The TruTone style bulbs are tuned to look like classic filaments, but the light they put out sits at a slightly different color than what a real tungsten bulb makes. Tungsten runs a bit warmer, sort of a golden orange, and when you put the two side by side in a dark room the LED strands read cooler and a little greenish. You especially see it in reflections off glass, which is exactly the situation you described, because the window doubles the difference for you.

I ran into the same problem a couple years back when I filled gaps on my tree with leftover mini strands. Deep in the branches by the trunk it looked fine, but any bulb visible through the outer layer or catching a reflection stood out like a sore thumb. What made it worse for me was warm white strands from two different manufacturers, so even two LED sets can disagree with each other.

If you want to keep the old incandescents, the trick is to bury them. Keep them well inside the tree pointing the same direction as everything else, so only their glow shows and not the bulbs themselves. Diffused glow mixes a lot better than a visible bulb does. Once your ornaments go on, the deeper strands will mostly disappear anyway, so you may get away with it this year. That said, if the mismatch bugs you every time you walk past the tree, you won't un-see it. Replacing those filler strands with matching TruTones is the only real fix. You don't have to do the whole tree at once, just swap out the fillers near the trunk and you'll be consistent all the way through. That's the route I ended up taking, and I stopped noticing anything except the tree after that.

We had this exact thing on our porch tree a couple years back, mixed strands and all. Ended up just moving the older sets out to the garage and sticking with one type per tree after that. One more thing to watch if you're running dimmers or a show controller: incandescents shift warmer as they dim and LEDs pretty much keep thier color, so the gap gets worse at low brightness. That's when mine really bugged me. At full on you could squint and pass it, at 30 percent it was obvious.

Seconding the poster who said the gap gets worse in reflections, same thing happened on our mantle garland. What really sold me on swapping mine out was taking a photo of the tree one night. In person I could sort of tune it out, but on the camera the old strands went noticeably yellow green next to the new ones and it looked way worse than it ever did live. If you're planning to send pics to family this year, that might be the thing that pushes you off the fence. I ended up just picking up two more boxes of the same type and calling it done.

This whole thread is making me look at my own tree differently now. I only ever bought one big box of lights years ago and strung them all at once, so I never had a reason to mix anything. Didn't even know the newer fake-filament ones coud look greenish next to the old ones. When you say bury the mismatched strands deeper in the tree, does that mean just stuffing them toward the middle trunk area, or actually rewinding them onto the branches a diffrent way? Mine are kind of looped around the outer branches and I'm not sure how you'd hide them without unstringing everything.

Update: tried the photo trick someone suggested and wow, the camera really does exaggerate it. In person I could mostly ignore the old strands, but in the shot they went clearly yellow next to the new ones. Moving them deeper toward the trunk helped at night, but the window reflection is still giving it away. Do you all swap a tree over all at once, or just replace a few strands each year untill it's done?