You can customize almost all the colors of the chart generated by WebChart platform now. In previous release, it's not possible to define the line color or bar color, it can only use the pre-defined colors. In latest release, if you did not customer the colors, then the same behaviour with previous release, else use the customized colors. Take a look at the following chart sample.
Following lines are the WCML file defination.
WEBCHART.XSLDOC=xsl/defchart.xsl
WEBCHART.TYPE=LINE
WEBCHART.SUBTYPE=LINE_SOLID
WEBCHART.SUBTYPE2=MARKER_CIRCLE
WEBCHART.WIDTH=480
WEBCHART.HEIGHT=240
WEBCHART.EDGECOLOR=148,140,181
WEBCHART.BACKCOLOR=216,193,213
WEBCHART.PLOTBACKCOLOR=207,207,120
WEBCHART.PLOTEDGECOLOR=blue
WEBCHART.COLORS=215,35,75
WEBCHART.QUERY_1=select trade_month, trade_count/10000 \
from trade_summary_monthly
I should ask a prefessional UI designer to choose the default colors, not choosed by a programer.