When assigning a color to a NodeShape with shacl-play:background-color (or volipi:color), and splitting diagrams, even if the NodeShape is not included in the diagram but just referred to, it should keep its color

[tfrancart]

test with this SHACL file URL : https://xls2rdf.sparna.fr/rest/convert?url=https%3A%2F%2Fdocs.google.com%2Fspreadsheets%2Fd%2F1NnWIuwdpjKiLLIMEOiIhr9pY3Oxb6BMF%2Fexport%3Fformat%3Dxlsx&noPostProcessings=true