My father won’t talk about the numbers 3-7-8-2-5 between the wrist and elbow blue as blood as his left forearm which technique is used in these excerpted lines?

The technique that has been used here is that of 'simile'.

Explanation:

'Simile' is a frequently used figure of speech which involves a comparison between two things that possess distinct features. Such a comparison is to make the reader or the listener feel the expanse of the idea being presented. By using this technique, the author makes sure that the reader of the listener understands both the meaning and the mood of the content.