An IFR C210 pilot reported they deviated from their assigned heading to avoid traffic climbing towards them.

Narrative

While on an instrument flight plan enroute from ZZZ to ZZZ1 to fly practice approaches; I took evasive action to avoid an aircraft identified on my ADS B that appeared to be climbing from below into my flight path from my 6 or 7 o'clock position. To avoid the traffic; I announced; 'I am turning to heading 300 to avoid traffic' and turned briefly from my assigned /vectored heading of 270 to heading 300. ATC was calling out traffic in front of me. I noticed an aircraft on ADS B climbing toward me from behind in what appeared to me to be a collision course. The altitude difference between my aircraft and the approaching aircraft was decreasing rapidly and it course appeared to be directly into my flight path. I announced; 'I am turning to heading 300 to avoid traffic.' I looked over my shoulder and saw a climbing aircraft pass behind me 'too close for comfort.' I then announced I was turning back to heading 270. ATC acknowledged and did not sound upset. A second ATC controller was on air very briefly who also acknowledged. My recollection is that his voice tone implied that my maneuver was acceptable. I was not given a phone number to call and the remainder of the flight and approaches at ZZZ1 and ZZZ were routine. I am not sure what I would do differently. I was concerned I would be climbed into from below. ATC was pretty busy with me and other aircraft. The situation seemed to me to rapidly become emergent and that there was not time for me to interrupt and ask; 'do you have the climbing traffic approaching at my 6 o'clock?' But perhaps I should have interrupted and asked. Or perhaps I should have added 'I am declaring a traffic emergency and turning to heading 300.' My voice tone may have said just that. I felt like I was reacting to an emergency. Or perhaps I should have trusted and relied on ATC and kept what looked to me to be a collision course. I work with a CFII maintaining proficiency and periodically getting IPCs (Instrument Proficiency Check). I will discuss with him.Please note that my altitude at the time may have been 4000 feet . I don't recall if the problem arose before or after I was assigned 4000 feet. Please note also that the distance from ZZZ1 a very rough guess.