The same style options are available as for
draw.io itself. You can find some guidelines here:
But generally you can find lots of info here:
For selecting arrow style, start
draw.io, apply the arrow you prefer to an edge. Then look at the style and find the start/endArrow style value.
Instead of straight=1 write curved=0, or completely remove curved, default is 0.
You color edges (connectors) the same as stencils (fillColor and strokeColor).