how to use vertex color node to control the particle alpha?

thanks，at addtive mode the alpha channel doesn't work whatever multiply  RGB or Alpha, i use the custom mode and set source to"sro to alpha"can fix the problem.but this time there is another problem,i link the refraction node to the main,when the alpha value of particle is 0,there is refraction,when the alpha value more then 0 ,the refraction effect is going down,when alpha is 255,no refraction.in this case i multiply texture alpha by RGB of vertex color,and use the particle color control the particle alpha.in this way maybe fix the problem . but sometimes for example make a swordtrail if i want to use vertex color to control particle color and alpha and use refraction also, Some problems may occur.