Hi Maruthi,
In the same system you used to develop your theme (using t-code /ui5/theme_designer), execute /ui5/theme_tool.
Once the window opens, you should see your theme displayed. Just to the right should be the word Info. Double click on the word.
A new window should open up with two lines showing. The first should start with sap-theme=. Using Ctrl-y, copy that entire line.
Using valid url syntax (& if there is already something after the webpage, ? if there is not.) paste it to the end of the launchpage url and execute the new url. This should override the existing theme used by the launchpage. Or at least this works for Launchpad (wave 2).
Regards, Mike
SAP Rapid Innovation Group - RIG