Fluxx 4 updated to version 1.0.1a
^ Buildcraft Compat to 7.1.5
^ Optifine to U D4
Type in the modpack name (Fluxx 4) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select Fluxx 4 from the list on the left. The launcher will handle everything else!