Hi Elenal,
Thanks for using Syncfusion Products.
You can achieve your requirement by applying the Triangle color as like in the following sample.
We have prepared a sample based on this and you can find the sample under the following location.
Sample :
http://www.syncfusion.com/uploads/redirect.aspx?file=100004_GTCTriangleBackground_580d37a3.rar&team=testingftpPlease let us know if this helps.
Regards,
Ramesh