Hi kidconcept, Welcome to Affinity Forums :) Those purple lines means the object you just clicked on is now a snapping candidate, that is, an object that you can align/snap other objects to.  In your case you have Show snapping candidates unchecked in the Snapping Manager thus the objects only do that quick flash (menu View ▸ Snapping Manager...) but you can have this enabled permanently checking that option. When you enable it, all objects that are snapping candidates will display a purple ou