Colors in the diagram are not readable with a dark swatch

[Stamo-Gochev]

Describe the bug
When using a dark swatch like default-main-dark, the text color of the connections of the Diagram are not readable.

To reproduce
Steps to reproduce the behavior:

1. Go to https://dojo.telerik.com/knMUyEPA

Expected behavior

Note that maybe the background should be dark. Otherwise, multiple colors are not visible, e.g. text color, the color of the connection (the line), etc.

Actual behavior

Affected package (please remove the unneeded items)

• theme-default
• theme-bootstrap
• theme-material
• theme-tasks

Affected suites (please remove the unneeded items)

• Kendo UI for jQuery

Additional context
Add any other context about the bug.