The purpose of this Iodine post is to illustrate some of the visual/chemical reactions of Potassium Iodine (KI) when mixed with various strengths of nitric acid.

10x – A solution of 1 drop nitric and 3 drops water produces no immediate reaction, but when another drop of nitric acid is added to this solution the previously dissolved KI produces an almost immediate (1 to 2 seconds) reaction as shown here.
The orange-red is also slowly (1 to 2 seconds during the reaction) forming the black crystals at left of image.

10x – After about 10 seconds into the reaction the Iodine changed from the red-orange to brown and these zillions of the black crystals.

10x – Another test where the solution is composed of 1 drop nitric acid and 1 drop water and a single KI crystal inserted into the solution.
An immediate boiling reaction took place, which was too fast to focus upon and capture, but was able to capture the tail-end of the reaction.
The beginning reaction was a deep red, which very quickly (2-3 seconds) became brown, and within 5 to 10 seconds the whole precipitation became black crystals as shown in next image.

10x – The completed reaction of the above image.
The Iodine has been liberated from the potassium and became these reduced black crystals of Iodine.

10x – Another test, where the solution consisted of 1 drop of nitric and 1 drop of water.
A single KI crystal inserted into the solution.
Only able to capture a portion of the beginning violent (boiling appearance) reaction

10x – After about 10 seconds the previous image became this image.

50x – A magnified image of the preceding photomicrograph, which tries to focus in on the black Iodine crystals. Unfortunately they are ill defined at this magnification.

70x – Further magnification of the preceding image begins to show the crystal shape of the liberated/reduced Iodine.
Higher magnification fails to improve upon these indiscreet black crystals because of insufficient lighting.

There are a metals that KI will precipitate as tiny black crystals from solutions of Nitric. Hydrochloric and Aqua-Regia.
When I conduct microchems with KI and any amount of HNO3 is present I am always cautious to draw conclusions when black crystals form, especially if there is any violent reactions or color reactions as pictured in this posting. I find it safer to make conclusions only after several more water diluted microchems.
PGMs dissolved in Aqua-Regia and the A-R is properly converted to a HCL solution produces a variety of black crystal precipitants with KI. Confirmation of the PGMs or any metal precipitant should be cross-checked with other precipitating reagents to reliably make conclusions.
When metals are in solutions of nitric acid solutions similar to or even quite diluted some metals can enhance the reactions and definitely the color combinations.

Click here to watch a few second, not entirely focused video of a reaction of KI crystals clinging to a toothpick tip being inserted into a solution of 1 drop nitric and 1 drop water on glass slide. The white background is to show as much color as practical.