Ang, if I understand you correctly - you think that the proper course at the mark for Yellow is to tack?
Well, then I'll change the picture a little.


PS .I can't load a picture :(

UPD 

The mark could be a windward mark, a finishing mark at the port end of a finishing line, a windward gate mark, or a limit mark that is not a rounding mark. In each of these situations, the boats shown are ‘on opposite tacks on a beat to windward’ and, therefore, rule 18 does not apply between them.

 I think Case 132 "Situation 2" illustrates the scenario

.Windward Mark: A rounding-mark on the current leg of the course which is upwind from a boat's current position, or relative to the starting-line, which would require a boat to sail on a beat to reach and round it on its proper side.

Well, thanks Angelo.
What about scenario #3?
Is it apply for the Case 132?

1. At position #2, Blue is first to enter the zone and is clear ahead of Green
   1. none of RRS 18.1's exclusions apply including 18.1 (a) and (b), therefore Case 132 doesn't apply
   2. Green owes Blue mark-room by RRS 18.2(b)
   3. Green must keep-clear of Blue by RRS 12
2. At position #3, Green enters the zone and Green is overlapped on the same tack to Windward of Blue
   1. RRS 18.2 (c) applies, thus Green still owes Blue mark-room as well as room for Blue to sail her proper course
   2. RRS 12 ceases to apply, RRS 11 starts to apply.  Green as windward boat must keep-clear of Blue
3. At position #3-1/2 Blue has tacked and has just passed head-to-wind from port tack to starboard tack (not shown, so use imagination)
   1. RRS 18.2 (b) & (c) cease to apply due to RRS 18.2(d)
      1. Green no longer owes Blue mark-room
   2. RRS 18 still applies between Blue and Green 
      1. least one of them is still in the zone and they have to leave the mark on the same side
      2. none of RRS 18.1's exclusions apply (thus Case 132 still doesn't apply)
      3. RRS 18.2(a) applies, Blue owes Green mark-room
         1. though they are on opposite tacks, they are overlapped because RRS 18 applies (see Clear Astern and Clear Ahead; Overlap)
   3. RRS 11 ceases to apply as Blue is now on Starboard Tack
   4. RRS 13 applies to Blue, she must keep clear of Green until she reaches a close-hauled starboard course
   5. RRS 10 does not apply while RRS 13 does, Blue is not ROW boat (yet)
   6. Green has not yet started to turn toward the mark or toward Blue
4. At position #4 - Blue completes her tack onto starboard
   1. RRS 13 ceases to apply, Blue kept clear of Green
   2. RRS 10 applies, Blue is ROW boat, Green must keep clear of Blue
   3. RRS 15 applies because Blue became ROW due to her action so must initially give Green room to keep clear
      1. it's close, but I think Blue gives Green room to keep clear by Green bearing away behind Blue
   4. RRS 18.2(a) applies, Blue owes Green mark-room which Blue fails to give.
   5. RRS 18.1(a) and (b) do not apply
      1. Green is not coming from a position of "over standing" and is not on a beat to windward
      2. It is neither Green or Blue's proper course to tack at the mark
      3. Case 132 still doesn't apply
5. DSQ Blue for failing to give Green 18.2(a) mark-room (assuming that Blue holds her course and Green falls off and ducks Blue)

Green is not coming from a position of "over standing" ...

•  in your Scenario 2 both boats approach and enter the zone on a beat to windward.   At that moment, we look at our RRS 18.1 tests, and look to the situations outlined in Case 132.  If you take your Scenario 2 drawing and delete position 1 and 2 (which is valid .. only consider 3 and 4), then it matches Case 132's Situation 2 exactly.
• in your Scenario 3, as I outlined above, each time 18.1's exclusion tests are applied, they fail (IMO).