Hello Jay Jose,
To modify existing theme:
1. On your Form in VS designer, drop the corresponding theme component from the VS toolbox (Telerik)
2. In the designer, select the control which theme you need to modify, open control's smart tag, then Select the Theme Name of the theme you wish to modify.
3. Again from the smart tag, click "Open Visual Style Builder" -> VSB will load the corresponding control with the current theme. Modify the color settings and save the theme file.
You can reuse this theme as specified in this KB article
To use the ThemeColorBlending feature, please refer to our online documentation.
the Telerik team