[planede]

Thanks! Maybe I didn't express myself clearly, but what I meant is more saturated "light blue" than what's available in sRGB, with the same brightness. For me #0000ff doesn't qualify as "light blue", so the point of comparison would be something like #aaaaff.

[Asooka]

If you're using a DCI-P3 (wide-gamut HDR) display, then #0000ff (or #aaaaff) in that display's colour space will be emitted as more saturated blue light than what an sRGB display is capable of. I am not sure if you will perceive them as exactly equally bright, brightness is subjective and depends on the reaction of your retina to the light hitting it, which is why #0000ff (blue) appears darker than #00ff00 (green), however the objective energy of the emitted light should be equal between displays of different gamuts, i.e. #ff0000, #00ff00, #0000ff should all result in the same amount of light being emitted in every correctly calibrated display regardless of the RGB primaries (aka gamut) it uses. The whole colour space topic is pretty deep, if you want to learn more about it and how colours are represented and converted between spaces, I encourage you to go and check out https://www.colour-science.org/ and linked resources.