diff --git a/src/components/sketch/SketchFields.tsx b/src/components/sketch/SketchFields.tsx
index 0a55d51..d82d080 100644
--- a/src/components/sketch/SketchFields.tsx
+++ b/src/components/sketch/SketchFields.tsx
@@ -145,7 +145,7 @@ export const SketchFields = ({
         <EditableInput
           style={{ input: styles.input, label: styles.label }}
           label="a"
-          value={Math.round(rgb.a * 100)}
+          value={Math.round((rgb.a ?? 1) * 100)}
           onChange={handleChange}
           dragLabel="true"
           dragMax="100"
diff --git a/src/types/colors.ts b/src/types/colors.ts
index abf1544..c92177a 100644
--- a/src/types/colors.ts
+++ b/src/types/colors.ts
@@ -4,21 +4,21 @@ export type Hsl = {
   h: number;
   l: number;
   s: number;
-  a: number;
+  a?: number;
 };
 
 export type Hsv = {
   h: number;
   s: number;
   v: number;
-  a: number;
+  a?: number;
 };
 
 export type Rgb = {
   r: number;
   g: number;
   b: number;
-  a: number;
+  a?: number;
 };
 
 export type Color = Hex | Hsl | Hsv | Rgb;