IGB displays insertions, deletions and mismatches as follows:
Insertions - Residues flanking insertion site are shown in black with a white background by default (purple on white here); triangular shapes between them point to the location of the inserted base(s) present in the aligned sequence but not in the reference. Select an insertion to display the sequence of inserted bases
Use the zoom stripe (shown in gray) as a guide to compare mismatches, deletions, and insertions between different read alignments and the reference.
Insertions, Deletions, and Mismatches in IGB
To re-create this scene in IGB: