This is an issue for a number of people, and until recently, little proof has been available. We've seen a number of 'yellow' Constructicons. America had them in the G2 line. Europe had a set of yellow Constructicons without the G2 moniker; ie, they could be called 'G1' Constructicons (or G1.5, if you cover them that way).
However...this is a page about the G1 French yellow Constructicons. As Artfire/Fracus tells us, they are a different yellow color, and come with G1 cardbackers and rubsigns.
So, in-effect, you have two different things when people are talking about yellow 'yellow G1' Constructicons. ;-)