Caelum is the Latin word from which we derive our word 'Cerulean', to describe a slightly greenish blue. That is what 'Caelum' blue is. It sits to the greenish side of neutral, although it is still very neutral itself. It has equal parts of yellow and red mixed in, but the yellow comes through just enough to make it slightly greener than, say, 'Dave Blue Eyes'. Level 6 is just lovely -- rich velvety looking blue.
NOTE: In general, use the individual color image as your guide. I have devoted many, many hours to adjusting the images to match the actual wool color, but the usual disclaimers (about colors appearing different on different monitors) apply.
HOW TO ORDER
The standard minimum size available at Ram in the Thicket is a 3" X 18" increment, and each of those represents one "item". So from each listing, order the total number of increments of that color you would like. If you order more than one 'item' of any color, I will send it out as one large piece.