This “เสียดาย เป็นสีที่ไม่ติดผ้า ย้อม..มิฉะนั้น คงได้ผ้าสีสวย..ค่ะ” may be fixable ;-) depending on the acidity of the ‘natural dye’ (Butterfly peas here). There are simple ‘dye fixers’ (mordants, such as salt, lime, vinegar, and alum) which we can boil the dyed fabrics in for an hour or so). For most plant based dyes boiling 1 part vinegar in 4 parts water may fix the dye. But don’t expect the color to be exactly the same ;-). In your case, try alum ;-)