## 1 Introduction  
Textile wet processing has long been considered to be a significant consumer of water and producer of effluents [1; 2]. In the conventional water-based reactive dyeing process, large amounts of salt were required to eliminate the repulsion force between dye molecules and the fiber surface, in order to enhance dye affinity and accelerate dye absorption [3]. To reduce effluent discharges and save environmental cost, alternatives such as low-salt or salt-free dyeing [4; 5; 6], dyeing using natural mordants [7; 8; 9], reusing wastewater for dyeing [10] and supercritical carbon dioxide dyeing [11; 12; 13] have been tried and are being used. For reasons related to the need for ecological friendliness, energy saving and safety of the working environment, the use of reverse micelles has also been considered as one of the mediums for non-aqueous dyeing [14; 15]. The reverse micelles are nanoscale spherical aggregates, which are self-assembled by certain surfactants in non-polar media [16; 17]. Their ability to solubilize a small amount of water in the interior region can provide a stable aqueous micro-environment (water-pool) in non-aqueous media. Attempts have been made to dye cotton with non-ionic reverse micelles in non-aqueous media [18; 19; 20]. A previous study has also investigated the feasibility of dyeing cotton in heptane and octane solvent using polyethylene glycol (PEG)-based nonionic reverse micelles [15]. In our previous study [15], we found that good dyeing results could be achieved in the case of dyeing cotton with reactive dyes without the use of salt as an exhausting agent. In conventional water-based dyeing of cotton with reactive dyes, large amounts of salt are required to promote dye exhaustion. The residual amount of salt in the effluent causes high loading in the subsequent wastewater treatment [21]. Since different colors are produced based on the primary colors (red, yellow and blue) and the appearance of the textile products is mostly a mixture of colors, color matching is of great importance in industrial applications. Computer color matching (CCM) is one of the modern advanced technologies combining the use of computer and colorimetry knowledge for the realization of color measure and recipe prediction [22]. It is a system involving the use of Kubelka-Munk theory and color difference formulae for colorant formulation. Computer color matching continues to be studied and applied in textile dyeing and printing [23; 24; 25; 26]. However, the feasibility of applying the computer color matching system on decamethylcyclopentasiloxane (D5) non-aqueous dyeing of cotton has not yet been studied. Color difference formulae are widely used for quality control, computer color matching, shade sorting and colorfastness evaluation. There are mainly two different usages of color difference formulae in computer color matching: (a) to determine the colorimetric closeness of the computed formula to the target; and (b) to calculate the metameric indices. In 1976, The International Commission on Illumination (CIE) recommended the use of two color difference formulae: CIELAB and CIELUV [27]. More advanced color difference formulae, such as CMC, BFD, CIE94 and LCD, were developed later, and finally, all datasets were used to develop the CIEDE2000 formula [28]. Several color difference formulae were still widely used in industrial applications, such as CIELAB, Hunter Lab, FMC-2, CMC and CIELUV [29]. With the use of such a system, the most accurate recipe, which is of good quality and is inexpensive, can be generated from the established database. The aesthetic appeal of the color of a textile product is often regarded as the first factor that arouses the interest of the customers. Therefore, the color performance during use is of great importance in terms of the expectations of the customers [30]. Color levelness is a description of the uniformity of the color shade in different places of the fabric [31; 32].