> But as much as I understood,
> it doesn't give you information on the fact that for example red is always
> co-localized with green but green is not always colocalized with red ? What
> kind of analysis  would I need to compare this between samples ?

Mander's coefficients are intended to give this kind of information,
see e.g. http://support.svi.nl/wiki/ColocalizationCoefficients
(coefficients interpretation at the end of the article).

Cheers,

jose.