I have a black row separator and a grey column separator, but because the row separator gets rendered first, the column separator appears over the top of it, causing what appears to be breaks in the row separator.
Is there any way to change the order these are rendered to prevent this?
I cannot tell you a nice and clean way to do this, however there is a "patch/hack" for this :) Inside your DataGridSkin, in the place where you redefine the default rowSeparator use can force a greater depth. This is definitely a patch since you hardcode the depth, but it will work.
<!--- @private -->
<fx:Component id="rowSeparator">
<s:Line depth="1000">
<s:stroke>
<s:SolidColorStroke color="0x0000FF" weight="5" caps="square"/>
</s:stroke>
</s:Line>
</fx:Component>