Liferay Theme generator tool is an easy way to create themes in Liferay v6.2 and 7. You would not need SDK for this but remember that there are some prequisities in terms of installation and configuration of few components before you can actually create theme and deploy to your Liferay.
Sharing this quick and short article on to highlight what are those key components to be installed.
High Level Steps required for configuration:
Theme for Liferay 6.2: Here are few screenshots of creating theme and then deploying the same on Liferay v6.2
Step 1. Run command yo liferay-theme and enter the name,id and select version. Please note that you will need provide the Liferay 6.2 Tomcat path
Step 2. Use gulp build command to build the theme
Step 3: Use gulp deploy command to deploy the same directly to the Liferay v6.2. Once this process is successfull, you will see the theme war file being directly copied to the deploy folder and then automatically getting deployed for you.