Walkthroughs + some compiled version differences:
https://strategywiki.org/wiki/Ys:_Ancient_Ys_Vanished/Walkthrough

Xanadu Cards and Falcom Interview Footage:
https://www.nicovideo.jp/watch/sm9068920

Falcom Interviews and some images:
https://shmuplations.com/ys/
http://blog.hardcoregaming101.net/2011/07/history-of-ys-interviews-by-john.html

Hiromasa Iwasaki blog:
http://www.highriskrevolution.com/gamelife/index.php?e=505

Prototype Ys images:
http://psyzans.com/Kura/Proto/Proto_1.html

The Tale of Caer Ys:
https://www.gutenberg.org/files/30871/30871-h/30871-h.htm#page_184

Things pulled during the music section:
https://www.squareenixmusic.com/features/interviews/yuzokoshiro.shtml
http://www.hardcoregaming101.net/ys-book-i-ii/?callback=in&code=NWIYNDEYYWMTOTAWZS0ZNZM3LWE1YZITNDNMOTM4M2EXOGI4&state=467a71f320ec4fed9e6eae11aec6c2fa

Numerous images and collected sources on Ys:
https://www.giantbomb.com/ys-the-vanished-omens/3030-14318/

1990: NINTENDO and the JAPANESE SOFTWARE boom | The Money Programme | Retro Computing | BBC Archive
https://www.youtube.com/watch?v=Wo5b0EpChH8&t=473s

On cultural and linguistic perception of color:
https://www.sapiens.org/language/color-perception/

*if you can't find a source, feel free to e-mail or DM me and I'll do my best to dig it up! I think I have it all listed, but I am unfortunately human