Pricing may vary across products that may be similar. This is due to the size, shape, and rarity of the colour glass chosen. For example, if a picture is made using a single piece of red, it will cost more than a larger picture that is made out of the more common colours.
I have included a colour rarity chart to make it easier to visualise the colours I may talk about in the descriptions of any product.
I have also included the link to the website where this chart is originally from so that you can learn more about each colour.