Colors vs Objects: One Harder Than The Other?

We just finished another attempt at color discrimination, using the cones this time, and we seem to be making pretty slow progress. Sometimes, it looks like he's getting the idea, but other times, he's still clearly in guessing mode, even when factoring out any excitement. With the object discrimination, he appears to be grasping things much faster. He's getting an understanding of the names of different objects and is making more sure choices.

I wonder if I'm running up against a sort of "natural limit", so to speak, in his intelligence. What I mean is that the task of distinguishing by color might not be something his senses and mind can readily pick up. Color might not be that important naturally while the shape of an object means a lot.

This is pretty interesting to me, and is something I haven't thought of until now, and this might be the first time I've seen any overt evidence of it - assuming I'm correct in my thinking at least.

If this is the case, then it's clear that he's regarding the objects themselves, and since the only difference is the color, the shape will be the same and he's uncertain of which of the two same-shaped objects I'm calling for. He's equally pulled to both, and makes a decision on other factors, such as location ("how did I get to it last time?"), position (a cone lying down looks different than one standing up, but I even take this away because both are standing up), distance ("maybe the close one is the one...", "maybe the far one...", "one word must mean the far one and one for the close one!") and which choice got him rewarded most recently. Color might not even entering his mind at this point.

This brings me to a couple initial ideas on how to proceed from here. One is that I might can test my theory. The other is that I forgo colors, at least for now, until I can think up (or find) a good way to teach colors to dogs. I haven't found any sites about it, and perhaps I'm finding out why first-hand. Being the type of person that hates to give up on something, I will likely test the theory first.

(Just as an aside, he reacted more to my verbal reward marker than the clicker. While he reacts to both, usually equally well, this time, it took "good boy" to get him to come get his reward. I wonder what that's about.)

Tests To Test The Theory

An idea I had was to have two large shapes. One being blue and one being yellow. The difference from the previous color testing would be that the shapes would also be different, say a circle and a triangle (this may give me an 'excuse' to teach him more Spanish, and learn more myself, as I could give the names of the shapes in Spanish).

Since he doesn't know the shapes by name, first, I'll teach him the shape names. Once it looks like he's grasping the shape names, I'll try to teach the color names with the same shapes. After that, I'll call for either the shape name or the color name and see if he gets it. I'll also see how fast he progresses, which could give some clues in addition.

Another idea I had would be to find a blue object and a yellow object that are two distinct shapes and sizes. Then do the above process on those two objects. This might be a challenge since I don't know if I have many blue or yellow things. Well, his food bowl is blue, but that will attract him for a different reason!

Even when we come up short in an attempt, he shows me something interesting to think about. I wonder how things will go when we get an opportunity to work on this.