And Blue-Card pay more attention to 4cards major than 5 cards minor, simply because 4-4 match major game is better than 3NT, and 55 match minor game worse than 3NT.

Pros:
1), quick to get the 4-4 match major.
2), side gains: after 1C opening, 1H/1S responds showing 5-cards, better than SAYC
3), for experts in championship, after 1C, quite safe using 1H/1S as psycho.
4), most important, the 1C opening got much clear info, so can use 2C/2D/2NT as weak first bids.

Cons:
1), partner can't pass with no support and about 5-9HP (if open 5cards major, just pass.)
2), will missing 5-3 minor match, but land on a 4-3 match major part-game contract
Although may be good in MP game, and landed on NT deal better than the minor deal. Also no system easy to show the 5cards minor.

For those don't like 4cards major opening, can choose LH Blue card.

====== Why put the strong hand with 1C opening instead 1D opening

Pros:
1), Anti interuption. In the very competitive biding, it not easy to show your hands is 15~19HP strong or game forcing strong after the 1D opening.
2), Since the 1C opening meaning no suit hands, so showing the major suit or jump a minor suit easy showing the very strong hands.

Cons:
1), In the competitive biding after 1C opening, can't using 2NT bid to show 2 minors (But if good partnership, you still can use 2NT to show the 2 minor hand and NT after double to show the very strong hand).
2), Also in the competitive biding after 1C opening, bid 2C or 2D showing good 5 cards minor, so for the strong hand, must jump or double first to show the minor suit.
3), If partner want to use psych 1H/1S after the 1C opening, that may confuse with yourself's strong hand with the major suit, instead confusing the oppenents.
4), Weak-2 responds after partner's 1C opening may block yourself.

For those good with big club systems, if have confidence handle the big 1D opening, still can put very strong hand in the 1D opening like that in the simple Blue Card. But still keep the 4-card major opening of the Deep Blue Card

====== Why 18~19HP 2NT for the Green Card
----Also an option for the Blue Card

1), Much offen happened than 20~21HP range, more useful.
2), Quite safe, if 11~14hp 1NT is quite popular, the 18~19hp 2NT certainly ok.
3), In SAYC, 1C/1D/1H open then jump to 2NT is somehow wasted, after partner response to your opening, already showed 5+HP, you with 18~19HP can bid 3NT directly.
4), Anti-interruption from opps, they don't have chance to give lead directing overcall.
This is the good point of the big 1NT opening, not easy for interruption.

====== The design of the 2 level bids after 1D opening
Principles:

1), for the hands quite often, not for the hands like 7600 distribution 0~2hp, you never meet once in whole life.
2), not easy to bid after 1H/1S response: like two long suits about 5HP.
3), not block your partner. In pre-emptive opennings, you got 60% block opps, 40% block your partner if in 1st or 2nd position, and 90% block opps if in 3rd position. But after your partner already showed a strong hand, you at high chance, will pre-emptive your partner's space.

There are so many options for choose, but based on probability and statistcs of boards generators, the blue cards using these bids for 9+HP, looking for the way for good slams.

======= After weak 1H response to 1D opening
Another option:
2S: for 15-17hpt, 1444, single spade

For 15-17hpt 4441 not spade single, rebid 1S, and for 4441 18-19, may rebid 1nt

======= the 1NT opening take care of 5-cards major

Cons: the transfer may missed a 5-3 major match, but landed on a 5-2 match contract.

Pros:
1), Avoid 1H responses to your 1D opening, the weak hand be the declarer.
2), Avoid the
1D------1S
2H/2S
or
1D------1H
2H
such sequences take off the bidding space.

======= The design of 1NT may have 5 cards heart.

2C: stayman
2D/2H/2S: transfer

-----after stayman:

2D: have 4cards major, no 5cards heart
2H: got 5cards heart
2S: minimum hand no major
2NT: maximum hand no major

-----after 1NT--2C--2D

2H: got 4-cards spade, about 7~8HP hands, let partner be the declarer
2S: got 4-cards heart, about 7~8HP hands, let partner be the declarer
2NT: got two majors.
3C: re-Stayman: asking for major, game forcing.
3D/3H: retransfer.

======= Also, 2NT opening can have 5 cards heart.

======= After 1C--1D--1H

2C: no Ace or King
2D: 1 Ace or King
2H: 2 Aces or Kings

====== After 2C:

2D: forcing, asking for 4 cards major
2H/2S: forcing, 5-cards suit
2NT: invitational
3C: stoping

====== After 2D:

2H/2S: forcing, 4-cards. Responds: 2NT no 3 cards support, other with 3 cards support
2NT: invitational
3D: stoping
3C: asking for strength. Responds: 3D weak, other strong.

==== Another choice for Green Card: multi-2C

2C openning for all weak-2s.

So can use opennings to reduce the load of 1D opening
2D for very strong hand, such as 9 winners
2H/2S for 15-17HP, real suit.