I found these themed messaging apk's while browsing the moto x forum. I tried 4 of them and all work fully including MMS.
Do not delete stock app. Rename it adding .bak or move it to sd or to the computer just in case you want it back.
Take any of the SMS zip files according to your choice from the site above. Extract it and find Mms_Signed in the system/priv-app. Copy Mms_Signed.apk to the Phone – SD. In Root explorer (or equal manager) change rights to rw and copy Mms_Signed.apk to the system/priv-app. Change permissions to rw-r-r. Reboot and find the new SMS app in the application drawer. That’s it.