Splines=ortho but the line is curving

Hi
I use graphviz to generate a visual graph.
I set splines=ortho, and set some edges with multiple colors(see image), such as:
a->b[color="#ff7f00:#33a02c:#1f78b4:#fdbf6f"]

The result like those below, each “color” concentrate together in turning point, and expand behind this point.
It make sense to draw paralleled color line?

Will you please provide the source for this graph and the output of dot -V