Unfortunately there is always this conflict between clear-delete-close-cancel so these are the worst icons to have to position next to each other whilst still being able to determine which icon means what action.
Considerations
The only occurrence of red amongst the icons should be associated with the delete because this is the destructive action and should not be able to be easily confused with the other actions. A cross is best for delete and it doesn't need a box.
Because the clear is an action with a subject, try to include a cue as to what is being cleared (eg using the common magnifying glass for the search icon), this will help differentiate with the other icons
Close and Cancel need to be differentiated by the fact that the cancel might be undoing any changes made and therefore returning with no change, where as close will save any changes.
I would actually re-interpret your need for close and cancel to being 'accept with save' and 'close-without-save'
So close is like Enter on the keyboard - accepting any changes made, and we can use some symbology from the popular return/enter key on a keyboard.
Close should not indicate any acceptance. I'm slightly uncertain about using the cross as it is visually related to delete in this case, but either the cross (black) or the minus sign would suffice and with a box around it.
You have included delete as the second item, but actually because of the destructive nature of delete, I would ideally position it either:
- at least at one end to halve the likelihood of an accidental hit when going for either
clear or accept-with-save
- preferably further separated from the other icons completely
Results
So here's the results after taking the above considerations on board:
