A file never stores a colour, only numbers. A colour space is the agreement that says which colour those numbers mean. Pick a colour and see it written in every common space; push the chroma up and watch it leave what a normal screen can show.
Every colour at lightness 60%, laid out by hue (across) and chroma (up). The solid area fits in sRGB, the space of most screens and the web's default. The faded band only fits in Display P3, the wider space of recent phones and Macs. Everything beyond is outside both. The ring is your colour.
Mixing halfway between two colours means different things depending on the space you do the maths in. Gradients, image resizing and blur all mix colours, so this is why the same edit can look muddy in one app and clean in another.