It appears customization of notes on class members is currently limited. In particular, you cannot specify the background colour for the note using the "standard" syntax:
note left of class_name::member/' cannot specify color anywhere on this line '/
this is a note
end note
You can instead customize a floating note and then attach it to the class attribute. It works but often changes the layout in unusual ways. Using the [hidden] connector between the classes is not always successful.
I (mis?)understand from the history that this feature is still a work in progress. Can we have a cleaner and more consistent syntax for this?
Please see the example here: http://www.plantuml.com/plantuml/uml/SoWkIImgAStDuKhEIImkLeY0qf5GEWfAEq9f9oZjp0LbkENdArHpAG11Kc8HLoqNLuI2JOskBaWSneo4CQ9W34SOmmdA09cNbr-Igf1OhE1dgA0Sd5tfb5EQ2ZQt92EpM0684XL0AhXIyr8W32wWGZqza4LMLY2x7O0oG8y00000
@startuml
class X
class Y
class Z
class A
class B
class C
class Foo {
bar
}
X <|-- Foo
X <|-- Y
X <|-- Z
X <|-- A
X <|-- B
X <|-- C
note as N1 #SkyBlue
this is a note
end note
N1 .. Foo::bar
@enduml