The arrow element is marked with one of the following classes:
.scheduler_default_link_arrow_left
.scheduler_default_link_arrow_right
.scheduler_default_link_arrow_down
.scheduler_default_link_arrow_up
Please note that if you set custom color link using the "color" link property the class will not be applied. That's a limitation of the CSS styling - the triangle is created using CSS borders and there is no way to override the color using inline styles.
If you want to apply a custom color, don't use "color" property of the link (https://api.daypilot.org/daypilot-link-data/) but specify custom "cssClass" and define the color using CSS.
The default class definitions look like this:
.scheduler_default_link_arrow_right:before { content: ''; border-width: 6px; border-color: transparent transparent transparent red; border-style: solid; width: 0px; height:0px; position: absolute; }
.scheduler_default_link_arrow_left:before { content: ''; border-width: 6px; border-color: transparent red transparent transparent; border-style: solid; width: 0px; height:0px; position: absolute; }
.scheduler_default_link_arrow_down:before { content: ''; border-width: 6px; border-color: red transparent transparent transparent; border-style: solid; width: 0px; height:0px; position: absolute; }
.scheduler_default_link_arrow_up:before { content: ''; border-width: 6px; border-color: transparent transparent red transparent; border-style: solid; width: 0px; height:0px; position: absolute; }