Update data model to allow for null values for soil layer colors. A NULL Color translates to Color.Empty, before both Color.Empty and a color with values (0;0;0;0) were both stored as 0 (Empty should be displayed as white, (0;0;0;0) as fully transparent black) Related to Issue [WTI-1298] git-svn-id: https://repos.deltares.nl/repos/WettelijkToetsInstrumentarium/trunk@12660 5a3db67b-de53-47b5-99c8-a1c30a6650e2