Use PROP:FillColor or PROP:Background or PROP:Color,1
?Field{prop:color,1} = color:lightblue
?Field{prop:fillcolor} = color:lightblue
Excerpt from the Clarion Help :
COLOR( color [, selected fore ] [, selected back ] )
COLOR Specifies display or print color.
color Specifies the background color (PROP:Background or PROP:FillColor, equivalent to {PROP:Color,1}). Foreground color is specified in the FONT attribute.
selected fore Specifies the default foreground color for the selected text on a control that can receive focus (PROP:SelectedColor, equivalent to {PROP:Color,2}). Not valid in a REPORT.
selected back Specifies the default background color for the selected text on a control that can receive focus (PROP:SelectedFillColor, equivalent to {PROP:Color,3}). Not valid in a REPORT.
The COLOR attribute (PROP:COLOR) specifies the default background and selected foreground and background colors.