This mod has the option to change the sprite and portrait art for all the villagers and some background characters to be more androgynous, including beach outfits. There's also variants for some characters, such as having darker skin or being in a wheelchair. Includes sprites for Emyn's Diverse Ginger Island.

What counts as 'androgynous' is pretty subjective and context specific, but my goal was to create art that can be read as intended to be male, female, or ambiguous, within the limits of my ability as a pixel artist. So I generally removed things like curvy chests, beards, sharp jaws, makeup etc that are strongly associated with only men or women in conventional sprite art, even though in real life the gender associations are more complicated, and there's no single 'androgynous' look.

I will definitely forget to update the screenshots to match any art changes, but will try and keep the screenshots of the base sprites and portraits up to date.

If you want to change a character's gender/dialogue/name etc as well as their appearance, use Gender Setter instead. For HD androgynous portraits, use Configurable HD Portraits.

Installation:
Install SMAPI and Content Patcher.
Download the file and unzip.
Put it in the Mods folder.

Customisation:
Either edit the config.json file or use Generic Mod Config Menu.
MiscImageEdits: Whether to edit a few minor background characters like the witch. 'true' or 'false'.
(Name)Images: Whether to edit the sprite and portrait for (Name). Generally 'true' or 'false', with a few exceptions:

• Vanilla/true: An androgynous version of the character with canon skin tone, no wheelchair, etc.   
• Wheelchair (Leah): Uses a wheelchair.
• Darker (Grandpa, Jas, Marnie, Sandy, Elliott, Caroline, Birdie, Professor Snail, Leo): Darker colouring.
• Islander (Birdie, Professor Snail, Leo): Indigenous versions as in Emyn's Diverse Ginger Island. 
  

I recommend only using LeoImages = Islander in conjunction with Emyn's Diverse Ginger Island, since otherwise he's written as a child and the sprite won't match. 

Genderswaps:
The default sprites will cause visual issues if you marry a character whose gender has been changed using a different mod. You can fix this by replacing Characters/(name).png with the genderswapped version in the Variants folder. For example, if you have set Abigail's gender to male with another mod, rename "Abigail_m" from the Variants folder to 'Abigail.png' and use it to replace Characters/Abigail.png in this or the relevant mod's assets folder.

Mod Conflicts:
This will conflict with any mods that also edit sprites and portraits, though you can turn off editing for any individual character. Some secondary images might get overwritten by mods that happen to overwrite the relevant file, eg there is a "cheering Marnie" sprite on the same spritesheet as various UI elements.

Credits and Recs:

I used/edited art from these open use mods, which are worth checking out if my edits of their art don't quite work for you:
Slightly Edited Portraits
talkohlooeys' Portraits
Slightly Cuter Character Sprites
Vanilla Facelift (Portrait Mod)
Shane Revised (CP)
Grandpa's Bed - Better Introduction for Content Patcher
Androgynous Kel
(CONTENT PACK UPDATED) Genderswap bachelorettes, which are in turn based on MCMC's portraits (note: Abigail is not open use)
Visual Crossing Sprite Overhaul
Visual Crossing Portrait Overhaul
Emyn's Diverse Ginger Island

I also edited an image from This Person Does Not Exist.

Here's some more mods with nice androgynous and/or diverse art:
Just Another Bachelors' Portraits Mod
Miowee's Portraits
Dong's Harvest Moon-Inspired Portraits (Content Patcher)
Leyalluna's Portraits (Content Patcher)
Genderbent Bachelorettes
Bachelor and Bachelorettes all portraits
Dreamburrows Elliott Portrait
Seasonal Younger Wizard - Moth's Vanilla Facelift-style Portraits
Shane anime portrait
gotama's Shane portrait without facial hair
Diverse Stardew Valley
Harvey Refined

Versions:
1.0: Initial upload
1.1: Minor visual tweaks. Nothing like staring at screenshots to make you notice things you want to change...
1.2: Redid bachelorettes to be more consistent with the rest of the art.
1.3: Fixed a bug with the alternate sprites.
1.3.1: Fixed some minor visual bugs, replaced art (Abigail sprites) that I realised were not open use.
1.3.2: Added androgynous Kel, and a few minor changes.
1.4: Redid a whole bunch of images, added Darker option for Sandy.
1.4.1: Added Islander/Emyn's Diverse Ginger Island images.
1.4.2: Fixed issue with Alex's hair, added compatibility to Kent Does The Dishes.
1.4.3: Minor visual edits.
1.4.4: Minor visual edits, some variable changes.
1.5: Compatibility with SDV Version 1.6
1.5.1: Fixed Bookseller