Uni Mitsubishi (Signo gel pens) and Pilot did choose not to disclose information about their products and companies (information on Uni : 2017; newest information on Pilot: 2021)
Faber-Castell is a distributor for Uni Ball and informed me (April 2021) that all the Uni Ball products they distribute, are free of animal derivatives; however, this concerns only the materials not Uni’s status (concerning the cruelty-free topic);
Speaking of Faber-Castell, these might work for you:
- Pitt artist pen in white (my opinion when I got them when they came out: not very opaque; buildable, for small highlights , best stored horizontally)
- watercolour pencils e.g. Albrecht Dürer; wet or dry application; of course pencils will last you practically a lifetime
- gelatos – watercolour in stick form; blendable with finger;
- oil pastel in white – should be very opaque
- soft pastel
- white pastel stick or Pitt pastel pencil; lovely over watercolour and alcohol markers …
Those are just examples (information from 2021); of course you can use any gouache or acylic paint (or pens, pastels, …) free of animal ingredients; my other brand informations on e.g. Culture Hustle (Stuart Semple), Liquitex , Golden Paints, Qor Watercolors and others are older (2017, 2018) , but you might want to look into them.
It depends also on what surface and other medium you are working with. I for example used gelatos in the past on canvas and like Pitt pastel pencils over watercolour and alcohol marker.