There's a difference. A chord is always composed of multiple notes. There's no single note that can sound like a chord. But a colour like yellow can be generated by a single wavelength or a combination of wavelengths that average out to yellow (so long as those wavelengths are not too far apart).

So in colour there is no sharp dividing line between a 'chord' and a 'note'. Some 'chords' look like 'notes' and some 'notes' look like 'chords'. Magenta is interesting because it's always a 'chord'.