here's the colors that light theme uses on here (they're generated internally by a bunch of Less functions that depend on the operator-configured primary color and stuff) in case anyone'd need to set it as a userstyle or somethin. Hopefully this post is not Too Long
:root {
--primary-color: #4d698e;
--secondary-color: #4d698e;
--body-bg: #fff;
--body-bg-shaded: #f7f7f7;
--body-bg-light: #fff;
--body-bg-faded: rgba(255,255,255,0.93);
--text-color: #111;
--link-color: #426799;
--heading-color: #111;
--muted-color: #667c99;
--muted-color-light: #8596ad;
--muted-color-dark: #000;
--shadow-color: rgba(0,0,0,0.35);
--control-bg: #e8ecf3;
--control-bg-light: #f2f4f8;
--control-bg-shaded: #dbe2eb;
--control-color: #667c99;
--error-color: #d83e3e;
--text-on-dark: #fff;
--text-on-light: #14191f;
--yiq-threshold: 150;
--header-bg: #fff;
--header-color: #4d698e;
--header-control-bg: #e8ecf3;
--header-control-color: #667c99;
--overlay-bg: rgba(77,105,142,0.9);
--code-bg: #f7f7f7;
--code-color: #5e5e5e;
--alert-bg: #fff2ae;
--alert-color: #ad6c00;
--alert-error-bg: #d83e3e;
--alert-error-color: #fff;
--alert-success-bg: #b4f1af;
--alert-success-color: #33722d;
--switch-on-color: #58a400;
--switch-off-color: #d0021b;
--enabled-color: #2ECC40;
--disabled-color: #FF4136;
--validation-error-color: #d83e3e;
--avatar-bg: var(--control-bg);
--badge-bg: var(--muted-color);
--badge-color: #fff;
--badge-hidden-bg: #888;
--usercard-bg: var(--control-bg);
--hero-bg: #e8ecf3;
--hero-color: #667c99;
--tooltip-bg: rgba(0,0,0,0.9);
--tooltip-color: #fff;
--online-user-circle-color: #7fba00;
--discussion-title-color: #7c7c7c;
--discussion-list-item-bg-hover: #f3f6f9;
--button-color: #667c99;
--button-bg: #e8ecf3;
--button-bg-hover: #d7dfea;
--button-bg-active: #c7d2e1;
--button-bg-disabled: #e8ecf3;
--button-primary-color: #fff;
--button-primary-bg: #4d698e;
--button-primary-bg-hover: #445d7d;
--button-primary-bg-active: #3b516d;
--button-primary-bg-disabled: #4d698e;
--control-danger-color: #d66;
--control-danger-bg: #fdd;
--control-danger-bg-hover: #ffc3c3;
--control-danger-bg-active: #faa;
--control-danger-bg-disabled: #fdd;
--muted-more-color: #aaa;
--muted-more-bg: rgba(170,170,170,0.3);
--muted-more-bg-hover: rgba(157,157,157,0.35);
--muted-more-bg-active: rgba(145,145,145,0.4);
--muted-more-bg-disabled: rgba(170,170,170,0.3);
--button-inverted-color: #667c99;
--button-inverted-bg: #fff;
--button-inverted-bg-hover: #f2f2f2;
--button-inverted-bg-active: #e6e6e6;
--button-inverted-bg-disabled: #fff;
--light-content-color: #fff;
--light-content-control-color: #fff;
--light-content-control-bg: rgba(0,0,0,0.1);
--light-content-control-bg-shaded: rgba(0,0,0,0.2);
--light-content-control-bg-fadedin: rgba(0,0,0,0.15);
--header-colored-color: #4d698e;
--header-colored-control-color: #667c99;
--header-colored-control-bg: #e8ecf3;
--header-colored-control-bg-shaded: #d7dfea;
--header-colored-control-bg-fadedin: #e8ecf3;
--tag-bg: #e8ecf3;
--tag-color: #667c99;
--button-toggled-color: #e8ecf3;
--button-toggled-bg: #667c99;
--button-toggled-bg-hover: #5c708a;
--button-toggled-bg-active: #52637a;
--button-toggled-bg-disabled: #667c99;
--following-bg: #ffea7b;
--following-color: #de8e00;
--ignoring-bg: #aaa;
--sticky-bg: #d13e32;
--lock-color: #888;
}