I dont' think you are being hypersensitive, especially about the purplish tinges. I do know that there is a huge error potential in blood pressure readings. The difference can be 25 to 30 mg but that is a bit more than you are seeing with those two readings. The way the blood pressure is take is very important. Different positions on the arm gives you different readings. Salt intake, stress levels, exercise level, and other factors can also make it fluctuate. I would be more concerned as to why the purple tinges to his lips, chin, and fingers.
Is your Dad on any blood pressure medication? If so is he taking it regularly? Other medications can cause changes in BP as well. Especially medications for colds and allergies. Time of day will give you different pressures if medication is related.
If you have a home BP monitor try taking the BP 3 to 5 times during the day, keeping a log, to see if you can find a pattern that relates to something such as food, medication, stress level. Take it several times in a row to see if there is any consistency. It should not fluctuate that dramatically only minutes apart. Then you can be armed with information to give the doctor.
There is also a condition called Pheochromocytoma which is marked by small adrenal tumors that can cause radical spikes in BP. There is a clonidine test and a 24 hour urine test that is a preliminary screening for this condition. It might be worth asking the doctor to do these test to rule out this condition.
My Dad has horrible circulation in his legs. He has limited feeling and color in his feet and toes but we know that is partly caused by the veins that were taken for his heart bypasses and his other vascular problems (he has vascular dementia). We have not noticed that kind of BP variations with him. Yet we have seen the purple tinges that you mentioned in areas.
Good luck in looking for an answer and I say go for that second opinion if you are not satisfied with the answers you are receiving. You are your Dad's best advocate
Love, deb