You can turn off the "coloured" squares by going into the settings found by clicking on your username at the top right then click on settings then Mail in the left hand column then untick the box "show avatar in the message list".
If you want to delete multiple emails try the following.
If you hold down the shift key then tick the box to the left of the first email you want to delete in the list of emails then scroll down using the scroll bar on the right hand side and tick the last email you want to delete then release the shift key. It will select all the emails in between. You can then click delete or drag and drop them into the Trash folder.
