change behaviour of GradientBuilder's .colors() and .html_colors()

README.md

@@ -294,12 +294,11 @@ All preset gradients are in the domain 0..1.
 grad1, err := colorgrad.NewGradient().
     HtmlColors("#18dbf4", "#f6ff56").
     Build()
-```
-![img](doc/images/gradient-normal.png)
 
-```go
 grad2 := grad1.Sharp(7)
 ```
+![img](doc/images/gradient-normal.png)
+
 ![img](doc/images/gradient-sharp.png)
 
 ```go

grad.go

@@ -97,33 +97,23 @@ func NewGradient() *GradientBuilder {
 }
 
 func (gb *GradientBuilder) Colors(colors ...color.Color) *GradientBuilder {
-	gb.colors = make([]colorful.Color, len(colors))
-	for i, v := range colors {
-		c, _ := colorful.MakeColor(v)
-		gb.colors[i] = c
+	for _, c := range colors {
+		col, _ := colorful.MakeColor(c)
+		gb.colors = append(gb.colors, col)
 	}
 	return gb
 }
 
 func (gb *GradientBuilder) HtmlColors(htmlColors ...string) *GradientBuilder {
-	colors := []colorful.Color{}
-	invalidColors := []string{}
-
 	for _, s := range htmlColors {
 		c, err := csscolorparser.Parse(s)
 		if err != nil {
-			invalidColors = append(invalidColors, s)
+			gb.invalidHtmlColors = append(gb.invalidHtmlColors, s)
 			continue
 		}
 		col, _ := colorful.MakeColor(c)
-		colors = append(colors, col)
+		gb.colors = append(gb.colors, col)
 	}
-
-	if len(invalidColors) > 0 {
-		gb.invalidHtmlColors = invalidColors
-	}
-
-	gb.colors = colors
 	return gb
 }
 

grad_test.go

@@ -105,6 +105,18 @@ func TestBasic2(t *testing.T) {
 	testStr(t, colors[2].Hex(), "#0000ff")
 
 	testStr(t, grad.At(math.NaN()).Hex(), "#ff0000")
+
+	// Custom colors #2
+	grad, _ = NewGradient().
+		HtmlColors("#00f", "#00ffff").
+		Colors(color.RGBA{255, 255, 0, 255}).
+		HtmlColors("lime").
+		Build()
+	colors = grad.ColorfulColors(4)
+	testStr(t, colors[0].Hex(), "#0000ff")
+	testStr(t, colors[1].Hex(), "#00ffff")
+	testStr(t, colors[2].Hex(), "#ffff00")
+	testStr(t, colors[3].Hex(), "#00ff00")
 }
 
 func TestError(t *testing.T) {