diff --git a/src/generate.ts b/src/generate.ts
index 304bb6e..aecc1b3 100644
--- a/src/generate.ts
+++ b/src/generate.ts
@@ -1,11 +1,9 @@
+import { mergeDeep } from "unocss"
+
 import { themeCSSVarKeys, themes } from "./themes"
 
-import type {
-  ThemeCSSVarKey,
-  ThemeCSSVars,
-  ThemeCSSVarsVariant,
-} from "./themes"
-import type { ShadcnThemeColor } from "./types"
+import type { ThemeCSSVarKey, ThemeCSSVars } from "./themes"
+import type { ColorOptions } from "./types"
 
 function generateLightVars(
   theme: "light" | "dark",
@@ -23,23 +21,28 @@ function generateLightVars(
   ].join("\n")
 }
 
-export function generateCSSVars(
-  color: ShadcnThemeColor | ThemeCSSVarsVariant,
-  radius: number,
-) {
+function getBuiltInTheme(name: string) {
+  const theme = themes.find((t) => t.name === name)
+  if (!theme) throw new Error(`Unknown color: ${name}`)
+  return theme.cssVars
+}
+
+function getColorTheme(color: ColorOptions) {
   let light: ThemeCSSVars
   let dark: ThemeCSSVars
 
   if (typeof color === "string") {
-    const theme = themes.find((t) => t.name === color)
-    if (!theme) throw new Error(`Unknown color: ${color}`)
-    const { cssVars } = theme
-    light = cssVars.light
-    dark = cssVars.dark
+    ;({ light, dark } = getBuiltInTheme(color))
+  } else if ("base" in color) {
+    ;({ light, dark } = mergeDeep(getBuiltInTheme(color.base), color.color))
   } else {
-    light = color.light
-    dark = color.dark
+    ;({ light, dark } = color)
   }
+  return { light, dark }
+}
+
+export function generateCSSVars(color: ColorOptions, radius: number) {
+  let { light, dark } = getColorTheme(color)
   const lightVars = generateLightVars("light", light, radius)
   const darkVars = generateLightVars("dark", dark, radius)
 
diff --git a/src/types.ts b/src/types.ts
index fbaf3f8..e13f01f 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -1,12 +1,21 @@
 import type { Theme as ShadcnTheme, ThemeCSSVarsVariant } from "./themes"
+import type { DeepPartial } from "unocss"
 
 export type ShadcnThemeColor = ShadcnTheme["name"]
 
-export interface PresetShadcnOptions {
+export type ColorOptions =
+  | ShadcnThemeColor
+  | ThemeCSSVarsVariant
+  | {
+      base: ShadcnThemeColor
+      color: DeepPartial<ThemeCSSVarsVariant>
+    }
+
+export type PresetShadcnOptions = {
   /**
    * @default 'zinc'
    */
-  color?: ShadcnThemeColor | ThemeCSSVarsVariant
+  color?: ColorOptions
   /**
    * @default 0.5
    */
diff --git a/test/generate.test.ts b/test/generate.test.ts
index de3bb22..8604c5a 100644
--- a/test/generate.test.ts
+++ b/test/generate.test.ts
@@ -61,4 +61,20 @@ describe("generate-theme-css-var", () => {
       ),
     ).toMatchFileSnapshot("custom.css")
   })
+
+  it("custom theme based on built in theme", () => {
+    expect(
+      generateCSSVars(
+        {
+          base: "zinc",
+          color: {
+            light: {
+              background: "0 1% 100%",
+            },
+          },
+        },
+        1,
+      ),
+    ).toMatchFileSnapshot("custom.css")
+  })
 })