A Few Questions About the Resistance Icons Below Monster Life Bars

I believe this has something to do with the monster's resistances. However, I'm not quite familiar with its nuances.

Does NOT having a Resistance mean they have 0% Resistance or Damage Reduction to that Damage Type?

Do the Gold Resistance Icons mean they're immune/heavily resistant to that damage type? Does the Silver Icon mean they have a minor resistance to that Damage Type? Are there other colors of icons that display the positive resistances on monsters?

If the icon is red, they have negative resistance, right? Are there varying intensities of red icons that display how much negative resistance the monster has?

This picture is from PoE2, in PoE1 negative resistance icons are on the left.

Given that nothing has changed since PoE1, all your assumptions are correct. Silver icon means positive resistnance, Gold icon means high positive resistance (I guess around 40% plus), red is neagative (the only negative one). No icon for 0 resistance. There are no monsters in both games that are (full) immune to some type of damage. But in PoE2 more monsters tend to be well resistant to certain damage types.

Bumping for visibility. Thanks for asking this, question I struggled with as a new player when starting.

Thanks, that's a helpful explanation.

Was also looking for this information, Thanks.

+1 bump. it helped.
Also, what's the % icon in the center?

Does this mean I should try and use more frost damage and abilities against this monster opposed to other types?

Yes, you are correct

Bump this!

I'd love to be able to hold mouse over these icons to discover what they mean. I've never learned PoE icons and I want to. But here are the reasons I haven't.

1. Status icons are very short in duration, resulting in me barely having time to see the icon.

2. The status icon often has a duration clock over it making it hard to see the icon.

3. PoE or PoE2 does not have the ability or have a tool tip to see what the status means. Nor is there an in-game status effect symbols page to review.

4. I'm too stressed trying to dodge (more PoE2) to even be able to see the status icons.

5. The status icons are too small.

6. The status icons are less than intuitive. Often what you might consider bleed is actually something else and bleed may look like something else.

7. Skills that apply effects don't indicate well enough the status icons they'll apply to monsters.

8. Some status icons have the same icon for vulnerable vs resistant, but just use a color to differentiate. The color isn't always intuitive or consistant, often leading to me questioning if the monster is resistant or vulnerable.

9. Status icons move. Often there are many icons and as they expire the move making it impossible to track.

10. Too many icons, too many statuses can be applied at once, resulting in it being very hard to know exactly what is applied.

11. It is hard to practice learning the symbols. Often time my builds apply statuses because of many different sources (and often based on chance), so swapping in/out a support gem to learn the skill may result in confusion when a rare ailment is applied randomly from a source you forgot about.

Some ideas:
Investigate corpse. You can investigate monsters you've slain to see what effects, ailments, and damage types it received before death.

Locking target and using alt to be able to get a tooltip when mouse hovering over symbols.

In-game status icons list page.

Put symbols on gems and skills. So for example if a gem causes bleeding, put the bleeding ailment symbol on it (and label it).

PoE2 has definitely improved things, but more should be done on this IMO.