So spin-1 doesn't refer to isospin which is what I suspected. It doesn't seem rightThey are both massless vector particles, they transform as vectors under rotations.
Thhis spin-1 does not refer to isospin, they have 0 isospin. When we refer to rotations is isospin space (isospin) we always denote this by adding iso. Isoscalar = spin 0 in isospin space (isopsin 0 particle), isovector = spin 1 in isopsin space (isospin 1 particle) etc.
It shouldn't matter what space we're in, an SU(3) octet is an SU(3) octet. It's weightsisospin are the eigenvalues of the \lambda^3 Gell-Mann matrix, only quarks have isopsin. Isopsin is a concept which relates to the (approximate) same mass of the up- and down-quarks.
The gluons form an octet in SU(3) colour space, the meson octet is SU(3) flavour space.
Things are beginning to clear up. What I was calling "isospin" looks like what you callYou will of course have things like "colour isospin" and "colour hypercharge" since the representations used for SU(3)_colour is the same as for SU(3)_flavour, but we don't speak about this as isospin due the possible confusion of flavour-isospin (which we only call isospin).
I don't think you are using "color isospin" in a proper way. All 8 gluons carry the same quantum numbers, except for color, and even there, there is no unique definition of color. I could replace the red-green-blue basis by one rotated in this space and there would be no observable consequence.Gluons do not have zero "color isospin"; (actually 2 do, 6 don't,...).
I think I do. Here's a list of the eigenvalues (any linear combination of these would also do)I don't think you are using "color isospin" in a proper way. All 8 gluons carry the same quantum numbers, except for color, and even there, there is no unique definition of color. I could replace the red-green-blue basis by one rotated in this space and there would be no observable consequence.
What do you think this "color isospin" is and does? Can you give us an example of what it operates on and what the eigenvalues are?