What's the best photo editor to fix colors in poorly lit photos?

Lightroom is pretty much the standard for this - the interface is simple and the exposure, contrast, and color temperature controls work well even with bad lighting photos. If you want something free, Darktable does a decent job, but it has a steeper learning curve. Adobe Photoshop works too, but it's overkill if you just want to adjust lighting - ends up being more expensive and complicated than you need.

If your photo is really dark, it's worth adjusting the exposure and shadows sliders more than just messing with color temperature - Lightroom does that really well, but honestly the bigger difference is in you understanding how to work the tone curve, because just cranking up contrast ends up blowing out the image. If you're looking for something that isn't a monthly subscription, try Capture One Express, which is free and has pretty precise controls for low-light photos, maybe even more intuitive than Darktable if you're just starting out.

What really helps is an editor that lets you control exposure non-destructively. The Lightroom they mentioned up there is genuinely good, but if you'd prefer something lighter, Capture One also works well with RAW and gives you plenty of control over shadows and highlights. What format are you working with - JPEG or RAW? Because if it's RAW you've got much more room to recover detail in the shadows.

The most important thing is not to rely only on the histogram - what you see on your screen can be completely misleading if your phone or monitor brightness is off. Always work with the image at 100% zoom to see the actual details, otherwise you'll end up ruining the photo trying to "fix" something that was already fine.

For low light, Capture One is brutal - the shadows and highlights controls are way more precise than anything else. It costs money, but if you're working with a bunch of photos like that, it's worth it. Affinity Photo also works great and it's a one-time purchase, no subscription. Darktable is free and has most of what you need, except the interface isn't as user-friendly - takes longer to learn, but it gets the job done.

The big mistake most people make is trying to save everything with saturation. A photo with poor lighting actually needs work on curves and shadow recovery, not just cranking up the color. Start there before you mess with saturation.