I assume you mean that when you look into the syringe, it seems clear? The absorbance of light by the dye depends on the total number of dye molecules present in the light path. You can change this either by changing the concentration of the dye, or the length of the light path. If the basin is 20 cms deep, and the syringe is only 0.5 cm diameter, then the difference in absorbance will be 40x. You might take a second syringe, fill  it with tap water and hold the two up side-by-side. You may see a difference (the limitation being the sensitivity of the human eye to changes in light intensity)