When attempting to install Alias Design 2015 on a system where Alias Surface 2015 is already installed, the installation option may be greyed out. This can occur if the Alias Surface was installed and the latest service packs where applied. To resolve this issue, you will need to remove the latest Alias Surface Service Packs.
Please see also the following link for other helpful suggestions:
Thanks to Philipp Wronski for sharing this tip with the community.