Double Variant for products

Hello everybody and thank you for reading,
I've tried to find something similar to what I'd need to achieve but until now I had no luck, I hope someone could guide me in the right direction.
I'm using Joomla 1.7.2 with hikashop starter 1.5.4, I have some products where I need to create two set of variants.
Example, the main product is Photoframe, the first set of variants will have value referring to the colours, the other set will refer to the dimension of the frame.
I've created the list of value and created the variants of the product with these, but when I have to create the other variants with the colours I'm able to select just from the previous values of dimension.
Here is what I mean, set of values for the variants with dimension

then the other one with the charecteristic colour

Then I manage the variants in the product...

But I see just the values of the first variants...



I still can't find any solution, what I'm doing wrong?
Thank you again for reading and for your advice.


G.

Thank you very much Nicolas, I'll try as soon as possible.