Gareth, I'm not so sure about the numbering as you are
Whilst there are two pieces with the same prefix (104) and a different suffix ( /1914 & /2106)on page 130 of the book "WMF Ikora and Myra Glass", there is also a fish (/4018) on page 126 with a 104 prefix and a different shaped vase (/1) on page 163 with a '104' prefix.
I conclude, therefore that the entire number has to be used when discussing a particular item.
My interpretation of 104/2106 is that there is no orange in the illustration , only a sort of mauve with some yellow hues, along with some highlighting.
Because of this I decided not to include the code in my post - only the attribution.